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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2018	Oct. 19, 2018
Entity Information [Line Items]
Entity Registrant Name	REGENERON PHARMACEUTICALS INC
Entity Central Index Key	0000872589
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Common Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		106,323,210
Class A Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,911,354

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 1,087,843	$ 812,733
Marketable securities	1,104,309	596,847
Accounts receivable - trade, net	1,665,737	1,538,642
Accounts receivable from Sanofi	269,271	193,684
Accounts receivable from Bayer	267,937	242,014
Inventories	1,039,679	726,138
Prepaid expenses and other current assets	284,807	224,972
Total current assets	5,719,583	4,335,030
Marketable securities	1,873,569	1,486,494
Property, plant, and equipment, net	2,524,446	2,358,605
Deferred tax assets	562,818	506,291
Other noncurrent assets	125,197	77,866
Total assets	10,805,613	8,764,286
Current liabilities:
Accounts payable	172,361	178,183
Accrued expenses and other current liabilities	781,924	637,162
Total current liabilities	1,417,230	1,135,483
Capital and facility lease obligations	707,203	703,453
Other noncurrent liabilities	194,033	152,073
Total liabilities	2,937,313	2,620,208
Stockholders' equity:
Preferred Stock, $.01 par value; 30,000,000 shares authorized; issued and outstanding - none	0	0
Additional paid-in capital	3,841,174	3,512,833
Retained earnings	4,433,904	2,946,733
Accumulated other comprehensive (loss) income	(10,519)	640
Treasury Stock, at cost; 3,990,021 shares in 2018 and 3,763,868 shares in 2017	(396,371)	(316,240)
Total stockholders' equity	7,868,300	6,144,078
Total liabilities and stockholders' equity	10,805,613	8,764,286
Class A Stock
Stockholders' equity:
Common stock	2	2
Common Stock
Stockholders' equity:
Common stock	110	110
Sanofi
Current liabilities:
Deferred revenue, current	246,812	177,746
Deferred revenue, noncurrent	421,196	379,936
Other
Current liabilities:
Deferred revenue, current	216,133	142,392
Deferred revenue, noncurrent	$ 197,651	$ 249,263

CONDENSED CONSOLIDATED BALANCE SHEET (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Stockholders' equity:
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	30,000,000	30,000,000
Preferred stock, issued (in shares)	0	0
Preferred stock, outstanding (in shares)	0	0
Treasury stock, outstanding (in shares)	3,990,021	3,763,868
Class A Stock
Stockholders' equity:
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	40,000,000	40,000,000
Common Stock, shares issued (in shares)	1,911,354	1,911,354
Common Stock, shares outstanding (in shares)	1,911,354	1,911,354
Common Stock
Stockholders' equity:
Common Stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common Stock, shares authorized (in shares)	320,000,000	320,000,000
Common Stock, shares issued (in shares)	110,288,595	109,477,222

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Revenues	$ 1,663,496	$ 1,500,673	$ 4,783,003	$ 4,289,780
Expenses:
Research and development	556,972	529,749	1,584,847	1,547,159
Selling, general, and administrative	369,232	306,766	1,064,886	910,520
Total expenses	1,036,573	940,747	2,966,661	2,749,000
Income from operations	626,923	559,926	1,816,342	1,540,780
Other income (expense):
Other income (expense), net	16,432	11,861	81,842	2,048
Interest expense	(7,494)	(6,182)	(20,851)	(19,084)
Total other income (expense)	8,938	5,679	60,991	(17,036)
Income before income taxes	635,861	565,605	1,877,333	1,523,744
Income tax expense	(41,206)	(177,288)	(253,286)	(498,752)
Net income	$ 594,655	$ 388,317	$ 1,624,047	$ 1,024,992
Net income per share - basic (in dollars per share)	$ 5.50	$ 3.64	$ 15.06	$ 9.66
Net income per share - diluted (in dollars per share)	$ 5.17	$ 3.32	$ 14.14	$ 8.84
Weighted average shares outstanding - basic (in shares)	108,033	106,706	107,828	106,108
Weighted average shares - diluted (in shares)	115,088	117,028	114,843	115,994
Statements of Comprehensive Income
Net income	$ 594,655	$ 388,317	$ 1,624,047	$ 1,024,992
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on marketable securities	752	21,485	(6,954)	36,645
Unrealized gain on cash flow hedges	341	2	2,388	30
Comprehensive income	595,748	409,804	1,619,481	1,061,667
Product
Revenues:
Revenues	1,025,488	957,367	3,009,779	2,739,745
Expenses:
Cost of goods sold	30,817	46,388	136,010	149,774
Collaboration and contract manufacturing
Expenses:
Cost of goods sold	79,552	57,844	180,918	141,547
Sanofi \| Product and service, other
Revenues:
Revenues	256,265	245,175	683,508	677,670
Bayer \| Product and service, other
Revenues:
Revenues	264,373	236,625	775,164	640,919
Other \| Product and service, other
Revenues:
Revenues	$ 117,370	$ 61,506	$ 314,552	$ 231,446

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 1,624,047	$ 1,024,992
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	105,441	110,960
Non-cash compensation expense	300,652	380,144
Other non-cash items, net	(82,694)	44,016
Deferred taxes	(33,521)	(108,242)
Changes in assets and liabilities:
Increase in Sanofi, Bayer, and trade accounts receivable	(228,605)	(359,829)
Increase in inventories	(281,624)	(235,645)
Increase in prepaid expenses and other assets	(87,817)	(28,209)
Increase (decrease) in deferred revenue	(29,462)	(59,116)
Increase (decrease) in accounts payable, accrued expenses, and other liabilities	179,852	(28,908)
Total adjustments	(157,778)	(284,829)
Net cash provided by operating activities	1,466,269	740,163
Cash flows from investing activities:
Purchases of marketable and other securities	(1,533,558)	(883,748)
Sales or maturities of marketable securities	644,103	379,275
Capital expenditures	(297,638)	(164,963)
Other	(10,000)	0
Net cash used in investing activities	(1,197,093)	(669,436)
Cash flows from financing activities:
Proceeds in connection with capital and facility lease obligations	0	57,000
Payments in connection with capital and facility lease obligations	0	(19,925)
Proceeds from issuance of Common Stock	87,408	226,892
Payments in connection with Common Stock tendered for employee tax obligations	(77,096)	(77,832)
Repurchases of Common Stock	(4,378)	0
Net cash provided by financing activities	5,934	186,135
Net increase in cash, cash equivalents, and restricted cash	275,110	256,862
Cash, cash equivalents, and restricted cash at beginning of period	825,233	547,703
Cash, cash equivalents, and restricted cash at end of period	$ 1,100,343	$ 804,565

Interim Financial Statements

9 Months Ended

Sep. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Interim Financial Statements

The interim Condensed Consolidated Financial Statements of Regeneron Pharmaceuticals, Inc. and its subsidiaries ("Regeneron," "Company," "we," "us," and "our") have been prepared in accordance with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all information and disclosures necessary for a presentation of the Company's financial position, results of operations, and cash flows in conformity with accounting principles generally accepted in the United States of America. In the opinion of management, these financial statements reflect all normal recurring adjustments and accruals necessary for a fair statement of the Company's financial position, results of operations, and cash flows for such periods. The results of operations for any interim period are not necessarily indicative of the results for the full year. The December 31, 2017 Condensed Consolidated Balance Sheet data were derived from audited financial statements, but do not include all disclosures required by accounting principles generally accepted in the United States of America. These financial statements should be read in conjunction with the financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017.

Certain reclassifications have been made to prior period amounts to conform with the current period's presentation.

We adopted Accounting Standards Codification ("ASC") 606, Revenue from Contracts with Customers, as of January 1, 2018. The Company adopted the standard using the modified retrospective method, and thus recognized a cumulative-effect adjustment to reduce Retained earnings and increase Deferred revenue on January 1, 2018 by $143.4 million, net of tax. Prior period amounts have not been adjusted in connection with the adoption of this standard.

The new standard did not have an impact on the recognition of revenue from product sales (see Note 2). However, the new standard has resulted in certain changes to the timing of revenue recognition related to our collaboration agreements (see Note 3). As a result of adopting ASC 606, non-refundable upfront payments, which were previously recognized ratably over the performance period, and substantive development milestones, which were previously recognized in the period when the milestone was achieved, will be recognized over the remaining performance period based on the Company's progress towards satisfying its identified performance obligation.

The following tables summarize the impacts of adopting ASC 606 on the Company's condensed consolidated financial statements as of and for the three and nine months ended September 30, 2018 compared with the guidance that was in effect before the change.



	September 30, 2018
Balance Sheet Data	As Reported		Adjustments			Balance Without Adoption of ASC 606
Inventories	$	1,039,679	$	17,518		$	1,057,197
Deferred tax assets	$	562,818	$	(15,027	)	$	547,791
Total assets	$	10,805,613	$	2,491		$	10,808,104
Accrued expenses and other current liabilities	$	781,924	$	(1,175	)	$	780,749
Deferred revenue from Sanofi (current)	$	246,812	$	(60,406	)	$	186,406
Deferred revenue - other (current)	$	216,133	$	(78,611	)	$	137,522
Total current liabilities	$	1,417,230	$	(140,192	)	$	1,277,038
Deferred revenue from Sanofi (noncurrent)	$	421,196	$	(28,078	)	$	393,118
Deferred revenue - other (noncurrent)	$	197,651	$	32,952		$	230,603
Total liabilities	$	2,937,313	$	(135,318	)	$	2,801,995
Retained earnings	$	4,433,904	$	137,809		$	4,571,713
Total stockholders' equity	$	7,868,300	$	137,809		$	8,006,109
Total liabilities and stockholders' equity	$	10,805,613	$	2,491		$	10,808,104



	Three Months Ended September 30, 2018									Nine Months Ended September 30, 2018
Consolidated Statement of Operations Data	As Reported			Adjustments			Balance Without Adoption of ASC 606			As Reported			Adjustments			Balance Without Adoption of ASC 606
Sanofi collaboration revenue	$	256,265		$	12,172		$	268,437		$	683,508		$	(5,159	)	$	678,349
Other revenue	$	117,370		$	24,574		$	141,944		$	314,552		$	(22,615	)	$	291,937
Total revenues	$	1,663,496		$	36,746		$	1,700,242		$	4,783,003		$	(27,774	)	$	4,755,229
Cost of collaboration and contract manufacturing	$	79,552		$	(17,518	)	$	62,034		$	180,918		$	(17,518	)	$	163,400
Income from operations	$	626,923		$	54,264		$	681,187		$	1,816,342		$	(10,256	)	$	1,806,086
Income before income taxes	$	635,861		$	54,264		$	690,125		$	1,877,333		$	(10,256	)	$	1,867,077
Income tax expense	$	(41,206	)	$	(2,663	)	$	(43,869	)	$	(253,286	)	$	4,630		$	(248,656	)
Net income	$	594,655		$	51,601		$	646,256		$	1,624,047		$	(5,626	)	$	1,618,421

The Company also adopted Accounting Standards Update ("ASU") 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, as of January 1, 2018. The amendments require companies to measure equity investments at fair value with changes in fair value recognized in net income. We have elected to measure certain equity investments we hold that do not have readily determinable fair values at cost minus impairment, if any, and adjust for observable price changes in orderly transactions for identical or similar investments of the same issuer. Upon adoption, the Company recognized a cumulative-effect adjustment, related to unrealized gains on equity securities, to reduce Accumulated other comprehensive income and increase Retained earnings on January 1, 2018 by $6.6 million. See Note 5 and Note 6.

Product Sales

9 Months Ended

Sep. 30, 2018

Revenues [Abstract]

Product Sales

Net product sales consist of the following:



	Three Months Ended September 30,				Nine Months Ended September 30,
Net Product Sales in the United States	2018		2017		2018		2017
EYLEA^®	$	1,021,782	$	953,279	$	2,997,829	$	2,727,132
ARCALYST^®	3,706		4,088		11,950		12,613
	$	1,025,488	$	957,367	$	3,009,779	$	2,739,745

The Company had product sales to certain customers that accounted for more than 10% of total gross product revenue for each of the three and nine months ended September 30, 2018 and 2017. Sales to each of these customers as a percentage of the Company's total gross product revenue are as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Besse Medical, a subsidiary of AmerisourceBergen Corporation	57	%	51	%	56	%	51	%
McKesson Corporation	36	%	29	%	37	%	29	%
Curascript SD Specialty Distribution, a subsidiary of Express Scripts	**		19	%	**		19	%
** Sales to Curascript SD Specialty Distribution represented less than 10% of total gross product revenue during the period.

Revenue from product sales is recognized at a point in time when our customer is deemed to have obtained control of the product, which generally occurs upon receipt by our distributors and specialty pharmacies. The Company's written contracts with its customers stipulate product is shipped freight on board destination (FOB destination).

The amount of revenue we recognize varies due to rebates, chargebacks, and discounts provided under governmental and other programs, distribution-related fees, and other sales-related deductions. In order to determine the transaction price, we estimate, utilizing the expected value method, the amount of variable consideration that we will be entitled to. This estimate is based upon contracts with customers and government agencies, statutorily-defined discounts applicable to government-funded programs, historical experience, estimated payer mix, and other relevant factors.

The following table summarizes the provisions, and credits/payments, for these sales-related deductions during the nine months ended September 30, 2018 and 2017.



	Rebates, Chargebacks, and Discounts			Distribution- Related Fees			Other Sales- Related Deductions			Total
Balance as of December 31, 2017	$	29,840		$	34,142		$	21,320		$	85,302
Provisions	159,060			155,523			29,730			344,313
Credits/payments	(145,813		)	(150,956		)	(35,756		)	(332,525		)
Balance as of September 30, 2018	$	43,087		$	38,709		$	15,294		$	97,090

Balance as of December 31, 2016	$	12,712		$	29,465		$	3,674		$	45,851
Provisions	121,599			140,860			33,518			295,977
Credits/payments	(108,811		)	(136,272		)	(21,444		)	(266,527		)
Balance as of September 30, 2017	$	25,500		$	34,053		$	15,748		$	75,301

Accruals for chargebacks and discounts are recorded as a direct reduction to accounts receivable. Accruals for rebates, distribution-related fees, and other sales-related deductions are recorded within accrued liabilities.

Collaboration Agreements

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Collaboration Agreements

We have entered into various agreements related to our activities to research, develop, manufacture, and commercialize product candidates and utilize our technology platforms. The Company earns collaboration revenue in connection with collaboration agreements to utilize our technology platforms and develop and/or commercialize product candidates. As described in Note 1, during the first quarter of 2018, we adopted ASC 606. Under the terms of the new standard, revenue is measured as the amount of consideration we expect to be entitled to in exchange for transferring promised goods or providing services to a customer, and is recognized when (or as) we satisfy performance obligations under the terms of a contract. Depending on the terms of the arrangement, we may defer the recognition of all or a portion of the consideration received because the performance obligations are satisfied over time.

Our collaboration agreements may require us to deliver various rights, services, and/or goods across the entire life cycle of a product or product candidate. In agreements involving multiple goods or services promised to be transferred to a customer, we must assess, at the inception of the contract, whether each promise represents a separate performance obligation (i.e., is "distinct"), or whether such promises should be combined as a single performance obligation.

The terms of these agreements typically include consideration to be provided to the Company in the form of non-refundable up-front payments, development milestones, payments for development activities, as well as payments for commercialization activities, sales milestones, and sharing of profits or losses arising from the commercialization of products.

At the inception of the contract, the transaction price reflects the amount of consideration we expect to be entitled to in exchange for transferring promised goods or services to our customer. We review our estimate of the transaction price each period, and make revisions to such estimates as necessary. In arrangements where we satisfy performance obligation(s) during the development phase over time, we recognize collaboration revenue over time typically using an input method on the basis of our research and development costs incurred relative to the total expected cost which determines the extent of our progress toward completion.

Under the Company's collaboration agreements, product sales and cost of sales for products which are currently approved are recorded by the Company's collaborators as they are deemed to be the principal in the transaction. The Company shares in any profits or losses arising from the commercialization of such products, and records its share of the variable consideration, representing net product sales less cost of goods sold and shared commercialization and other expenses, as collaboration revenue in the period in which such underlying sales occur and costs are incurred by the collaborator.

In arrangements where the collaborator records product sales, the Company may be obligated to use commercially reasonable efforts to supply commercial bulk product to its collaborators, and may be reimbursed for its manufacturing costs as commercial product is shipped to its collaborators; however, recognition of such cost reimbursements as collaboration revenue is deferred until the product is sold by the Company's collaborators to third-party customers. In addition, we may also be reimbursed for a portion of costs incurred for other commercial-related activities, which are recorded as collaboration revenue in the period in which such costs are incurred.

a. Sanofi

The collaboration revenue we earned from Sanofi is detailed below:



	Three Months Ended September 30,						Nine Months Ended September 30,
Sanofi Collaboration Revenue	2018			2017			2018			2017
Antibody:
Reimbursement of Regeneron research and development expenses	$	76,150		$	128,539		$	201,026		$	421,056
Reimbursement of Regeneron commercialization-related expenses	103,666			90,339			292,756			251,002
Regeneron's share of losses in connection with commercialization of antibodies	(38,924		)	(98,315		)	(182,595		)	(328,998		)
Other	33,166			41,848			82,150			84,338
Total Antibody	174,058			162,411			393,337			427,398
Immuno-oncology:
Reimbursement of Regeneron research and development expenses	74,797			61,649			225,675			188,408
Reimbursement of Regeneron commercialization-related expenses	3,236			1,115			6,507			1,864
Other	4,174			20,000			57,989			60,000
Total Immuno-oncology	82,207			82,764			290,171			250,272
	$	256,265		$	245,175		$	683,508		$	677,670

Antibodies

In November 2007, the Company entered into a global, strategic collaboration with Sanofi to discover, develop, and commercialize fully human monoclonal antibodies (the "Antibody Collaboration"). The Antibody Collaboration was governed by the companies' Discovery and Preclinical Development Agreement ("Antibody Discovery Agreement") and a License and Collaboration Agreement (each as amended). Pursuant to the Antibody Discovery Agreement, Sanofi agreed to fund up to $130.0 million of the Company's research activities in 2017. The Company's Antibody Discovery Agreement with Sanofi ended on December 31, 2017 without any extension and, therefore, funding from Sanofi under the Antibody Discovery Agreement ceased after 2017. Under the License and Collaboration Agreement, following receipt of the first positive Phase 3 trial results for a co-developed drug candidate, subsequent Phase 3 trial-related costs for that drug candidate ("Shared Phase 3 Trial Costs") are shared 80% by Sanofi and 20% by Regeneron. Consequently, during the three months ended September 30, 2018 and 2017, the Company recognized as research and development expense $13.4 million and $22.6 million, respectively, and during the nine months ended September 30, 2018 and 2017, the Company recognized as research and development expense $37.2 million and $68.2 million, respectively, its share of antibody development expenses that Sanofi incurred related to Praluent^®(alirocumab), Kevzara^® (sarilumab), and Dupixent^® (dupilumab). All other agreed-upon worldwide development expenses incurred by both companies are funded by Sanofi.

Effective January 7, 2018, the Company and Sanofi entered into a letter agreement (the "Letter Agreement") in connection with, among other matters, the allocation of additional funds to certain activities relating to dupilumab and REGN3500 (collectively, the "Dupilumab/REGN3500 Eligible Investments"). Refer to the "Immuno-Oncology" section below for further details regarding the Letter Agreement. During the third quarter of 2018, Sanofi elected to sell, and we elected to purchase (in cash), 10,766 shares of the Company's Common Stock in connection with Sanofi's funding obligation for Dupilumab/REGN3500 Eligible Investments. Consequently, we recorded the cost of the shares received, or $4.4 million, as Treasury Stock during the third quarter of 2018.

In March 2017, the U.S. Food and Drug Administration ("FDA") approved Dupixent for the treatment of adult patients with moderate-to-severe atopic dermatitis, and in September 2017, the European Commission granted marketing authorization for Dupixent for use in adults with moderate-to-severe atopic dermatitis who are candidates for systemic therapy. In October 2018, the FDA also approved Dupixent as an add-on maintenance therapy in patients with moderate-to-severe asthma aged 12 years and older with an eosinophilic phenotype or with oral corticosteroid-dependent asthma. In May 2017, the FDA approved Kevzara for the treatment of adult patients with moderately to severely active rheumatoid arthritis, and in June 2017, the European Commission granted marketing authorization for Kevzara for the treatment of rheumatoid arthritis in adult patients.

Sanofi leads commercialization activities for products developed under the Antibody Collaboration, subject to the Company's right to co-promote such products. In addition to profit and loss sharing, the Company is entitled to receive up to $250.0 million in sales milestone payments, with milestone payments commencing only if and after aggregate annual sales outside the United States exceed $1.0 billion on a rolling twelve-month basis. The amount of variable consideration related to such share of profits and losses and sales milestones is deemed to be constrained as of September 30, 2018, and therefore has not been included in the transaction price.

The Company's significant promised goods and services consist of providing research and development services, including the manufacturing of clinical supplies, and providing commercial-related services, including the manufacturing of commercial supplies. As it relates to the Antibody Collaboration, "Reimbursement of Regeneron commercialization-related expenses" in the table above represents reimbursement of internal and external costs in connection with commercializing Praluent, Kevzara, and Dupixent. As we recognize Sanofi antibody collaboration revenue in an amount equal to the amount we have the right to invoice and such amount corresponds directly with the value to Sanofi of our performance to date, we do not disclose the value of the transaction price allocated to our remaining unsatisfied performance obligations.

The following table summarizes accounts receivable and deferred revenue information in connection with the Company's Antibody Collaboration with Sanofi:



	September 30,		December 31,
	2018		2017
Accounts receivable	$	187,704	$	121,001
Deferred revenue	$	199,523	$	117,682

Significant changes in deferred revenue balances are as follows:



	Nine Months Ended September 30, 2018
Increase due to shipments of commercial supplies to Sanofi	$	178,608
Revenue recognized that was included in deferred revenue at the beginning of the period	$	(96,767	)

Immuno-Oncology

In July 2015, the Company and Sanofi entered into a collaboration to discover, develop, and commercialize antibody-based cancer treatments in the field of immuno-oncology (the "IO Collaboration"). The IO Collaboration is governed by an Immuno-oncology Discovery and Development Agreement ("IO Discovery Agreement"), and an Immuno-oncology License and Collaboration Agreement ("IO License and Collaboration Agreement"). In connection with the IO Discovery Agreement, Sanofi made a $265.0 million non-refundable up-front payment to the Company. The term of the IO Discovery Agreement will continue through the later of five years from the effective date of the IO Collaboration or the date our budget for IO Discovery activities, which has been agreed to with Sanofi, is exhausted, subject to Sanofi's option to extend it for up to an additional three years for the continued development (and funding) of selected ongoing programs.

In connection with the IO License and Collaboration Agreement, Sanofi made a $375.0 million non-refundable up-front payment to the Company. Under the terms of the IO License and Collaboration Agreement, the parties are co-developing Libtayo^® (cemiplimab), an antibody targeting the receptor known as programmed cell death protein 1 (PD-1). The parties share equally, on an ongoing basis, development expenses for Libtayo up to a total of $1.640 billion, an increase of $990.0 million over the budget set forth in the original IO License and Collaboration Agreement. Pursuant to the Letter Agreement, the Libtayo development budget has been increased and the Company has agreed to allow Sanofi to satisfy in whole or in part its funding obligations with respect to Libtayo development and Dupilumab/REGN3500 Eligible Investments by selling up to an aggregate of 1,400,000 shares of our Common Stock directly or indirectly owned by Sanofi through September 30, 2020. If Sanofi desires to sell shares of our Common Stock during the term of the Letter Agreement to satisfy a portion or all of its funding obligations for the Libtayo development and/or Dupilumab/REGN3500 Eligible Investments, we may elect to purchase, in whole or in part, such shares from Sanofi. If we do not elect to purchase such shares, Sanofi may sell the applicable number of shares (subject to certain daily and quarterly limits) in one or more open-market transactions. During the second and third quarters of 2018, Sanofi elected to sell, and we elected to purchase (by issuing a credit towards the amount owed by Sanofi), 121,601 and 93,786 shares, respectively, of the Company's Common Stock to satisfy Sanofi's funding obligation related to Libtayo development costs. Consequently, we recorded the cost of the shares received, or $37.6 million and $38.1 million as Treasury Stock during the second and third quarters of 2018, respectively.

The Company has principal control over the development of Libtayo and leads commercialization activities in the United States, while Sanofi will lead commercialization activities outside of the United States and the parties will equally share profits from worldwide sales. On September 28, 2018, the FDA approved Libtayo for the treatment of patients with metastatic or locally advanced CSCC, and Sanofi has exercised its option to co-promote Libtayo in the United States. The Company will be entitled to a milestone payment of $375.0 million in the event that global sales of certain licensed products targeting PD-1 (including Libtayo), together with sales of any other products licensed under the IO License and Collaboration Agreement and sold for use in combination with any of such licensed products targeting PD-1, equal or exceed $2.0 billion in any consecutive twelve-month period. The amount of variable consideration related to such milestone is deemed to be constrained as of September 30, 2018, and therefore has not been included in the transaction price.

In August 2018, we and Sanofi entered into a license agreement with Bristol-Myers Squibb Company, E. R. Squibb & Sons, L.L.C., and Ono Pharmaceutical Co., Ltd. to obtain a license under certain patents owned and/or exclusively licensed by one or more of those parties that includes the right to develop and sell Libtayo. Under the agreement, we and Sanofi became obligated to make an up-front payment of $20.0 million and pay royalties of 8.0% on worldwide sales of Libtayo through December 31, 2023, and royalties of 2.5% from January 1, 2024 through December 31, 2026. The up-front payment and royalties are shared equally by us and Sanofi.

At the inception of the IO Collaboration, the Company's significant promised goods and services consisted of a license to certain rights and intellectual property and providing research and development services, including the manufacturing of clinical supplies. The Company concluded that the license was not distinct, primarily as a result of (i) Sanofi being unable to benefit from the license on its own or together with other resources that are readily available as the license provides access to Regeneron's complex and specialized know-how and (ii) the research and development services, including manufacturing in support of such services, were expected to significantly modify the initial license. Therefore, the promised goods and services were considered a single performance obligation. Consequently, the $640.0 million in aggregate up-front payments made by Sanofi during 2015 in connection with the execution of the IO Collaboration has been recorded as deferred revenue and has been included in the transaction price at the inception of the contract. "Other" Sanofi immuno-oncology revenue in the Sanofi Collaboration Revenue table above primarily includes recognition of deferred revenue from the $640.0 million of up-front payments.

As it relates to the IO Collaboration, "Reimbursement of Regeneron commercialization-related expenses" in the table above represents reimbursement of costs by Sanofi in connection with the commercialization of Libtayo outside of the United States.

The following table summarizes accounts receivable and deferred revenue information in connection with the Company's IO Collaboration with Sanofi:



	September 30,		December 31,
	2018		2017
Accounts receivable	$	75,627	$	59,274
Deferred revenue	$	468,484	$	440,000

Significant changes in deferred revenue balances are as follows:



	Nine Months Ended September 30, 2018
Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606	$	93,643
Revenue recognized that was included in deferred revenue at the beginning of the period	$	(65,159	)

The aggregate amount of the transaction price under the IO Collaboration allocated to the Company's performance obligation that was unsatisfied (or partially unsatisfied) as of September 30, 2018 was $1,562.9 million. This amount is expected to be recognized as revenue over the remaining period the Company is obligated to satisfy its performance obligation in connection with performing development activities.

b. Bayer

EYLEA outside the United States

Revenue earned in connection with our Bayer EYLEA collaboration is as follows (note that the table excludes amounts in connection with our Bayer Ang2 antibody and PDGFR-beta antibody collaboration agreements, which are described below):



	Three Months Ended September 30,				Nine Months Ended September 30,
Bayer EYLEA Collaboration Revenue	2018		2017		2018		2017
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	243,152	$	205,367	$	721,522	$	571,126
Reimbursement of Regeneron EYLEA development expenses	1,676		6,053		8,811		10,833
Other	20,764		15,714		45,321		36,910
	$	265,592	$	227,134	$	775,654	$	618,869

Under the terms of the license and collaboration agreement with Bayer for the global development and commercialization outside the United States of EYLEA, Bayer markets EYLEA outside the United States, where, for countries other than Japan, the companies share equally in profits and losses from sales of EYLEA. In Japan, the Company is entitled to receive a tiered percentage of between 33.5% and 40.0% of EYLEA net sales. In addition, the Company and Bayer share the funding of agreed-upon EYLEA development costs.

The following table summarizes accounts receivable and deferred revenue information in connection with the Company's EYLEA collaboration with Bayer:



	September 30,		December 31,
	2018		2017
Accounts receivable	$	269,155	$	241,153
Deferred revenue	$	85,504	$	68,734

Significant changes in deferred revenue balances are as follows:



	Nine Months Ended September 30, 2018
Increase due to shipments of commercial supplies to Bayer	$	47,958
Revenue recognized that was included in deferred revenue at the beginning of the period	$	(31,188	)

Ang2 antibody and PDGFR-beta antibody outside the United States

In 2016, the Company entered into an agreement with Bayer governing the joint development and commercialization outside the United States of an antibody product candidate to angiopoietin-2 (Ang2), REGN910-3, for the treatment of ocular diseases or disorders. In connection with the agreement, Bayer made a non-refundable up-front payment and paid a portion of our global development costs and development costs exclusively for the territory outside the United States. In the fourth quarter of 2017, the Company reported that results from two Phase 2 studies of REGN910-3 did not provide sufficient differentiation to warrant Phase 3 development. Therefore, during the fourth quarter of 2017, the Company accelerated and recognized the remaining amount of deferred revenue from the $50.0 million up-front payment (which was initially recorded as deferred revenue) received from Bayer as the Company deemed its performance obligation to be satisfied. On November 1, 2018, the Company and Bayer agreed to terminate this collaboration agreement.

In 2014, the Company entered into a license and collaboration agreement with Bayer governing the joint development and commercialization outside the United States of an antibody product candidate to Platelet Derived Growth Factor Receptor Beta (PDGFR-beta), REGN2176-3. Effective in the first quarter of 2017, the Company discontinued clinical development of REGN2176-3, and on July 31, 2017, the Company and Bayer agreed to terminate this collaboration agreement.

c. Teva

In September 2016, the Company and Teva entered into a collaboration agreement (the "Teva Collaboration Agreement") to develop and commercialize fasinumab globally, excluding certain Asian countries that are subject to our collaboration agreement with Mitsubishi Tanabe Pharma Corporation. In connection with the Teva Collaboration Agreement, Teva made a $250.0 million non-refundable up-front payment in September 2016. The Company leads global development activities, and the parties share development costs equally, on an ongoing basis, under a global development plan. The Company is also responsible for the manufacture and supply of fasinumab globally.

During the second and fourth quarters of 2017, the Company earned, and recognized as substantive milestones, development milestones of $25.0 million and $35.0 million, respectively, from Teva upon initiation of two Phase 3 trials. During the third quarter of 2018, the Company achieved a development milestone of $60.0 million. The Company is entitled to receive up to an aggregate of $340.0 million in additional development milestones and up to an aggregate of $1,890.0 million in contingent payments upon achievement of specified annual net sales amounts; the amount of variable consideration related to such milestones is deemed to be constrained as of September 30, 2018, and therefore has not been included in the transaction price.

At the inception of the Teva Collaboration Agreement, the Company's significant promised goods and services consisted of a license to certain rights and intellectual property and providing research and development services, including the manufacturing of clinical supplies. The Company concluded that the license was not distinct, primarily as a result of (i) Teva being unable to benefit from the license on its own or together with other resources that are readily available as the license providing access to Regeneron's complex and specialized know-how and (ii) the research and development services, including manufacturing in support of such services, were expected to significantly modify the initial license. Therefore, the promised goods and services were considered a single performance obligation. Consequently, the $250.0 million up-front payment and development milestones received or receivable from Teva, as described above, have been recorded as deferred revenue and have been included in the transaction price.

The Company recognized $69.2 million and $40.2 million of revenue for the three months ended September 30, 2018 and 2017, respectively, and $196.6 million and $141.0 million of revenue for the nine months ended September 30, 2018 and 2017, respectively, in connection with the Teva Collaboration Agreement.

The following tables summarize accounts receivable and deferred revenue information in connection with the Teva Collaboration Agreement:



	September 30,		December 31,
	2018		2017
Accounts receivable (recorded within Prepaid expenses and other current assets)	$	87,985	$	71,297
Deferred revenue	$	213,660	$	197,357

Significant changes in deferred revenue balances are as follows:



	Nine Months Ended September 30, 2018
Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606	$	48,216
Increase due to amounts invoiced, excluding amounts recognized as revenue during the period	$	33,774
Revenue recognized that was included in deferred revenue at the beginning of the period	$	(67,771	)

The aggregate amount of the transaction price under the Teva Collaboration Agreement allocated to the Company's performance obligation that was unsatisfied (or partially unsatisfied) as of September 30, 2018 was $520.1 million. This amount is expected to be recognized as revenue over the remaining period the Company is obligated to satisfy its performance obligation in connection with performing development activities.

Net Income Per Share

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Net Income Per Share

The Company's basic net income per share amounts have been computed by dividing net income by the weighted average number of shares of Common Stock and Class A Stock outstanding. Net income per share is presented on a combined basis, inclusive of Common Stock and Class A Stock outstanding, as each class of stock has equivalent economic rights. Diluted net income per share includes the potential dilutive effect of other securities as if such securities were converted or exercised during the period, when the effect is dilutive. The calculations of basic and diluted net income per share are as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Net income - basic and diluted	$	594,655	$	388,317	$	1,624,047	$	1,024,992

(Shares in thousands)
Weighted average shares - basic	108,033		106,706		107,828		106,108
Effect of dilutive securities:
Stock options	7,027		9,809		6,999		9,386
Restricted stock	28		513		16		500
Dilutive potential shares	7,055		10,322		7,015		9,886
Weighted average shares - diluted	115,088		117,028		114,843		115,994

Net income per share - basic	$	5.50	$	3.64	$	15.06	$	9.66
Net income per share - diluted	$	5.17	$	3.32	$	14.14	$	8.84

Shares which have been excluded from diluted per share amounts because their effect would have been antidilutive include the following:



	Three Months Ended September 30,		Nine Months Ended September 30,
(Shares in thousands)	2018	2017	2018	2017
Stock options	14,446	4,515	14,821	8,892
Restricted stock	—	—	57	—

Marketable Securities

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities as of September 30, 2018 and December 31, 2017 consist of both available-for-sale debt securities of investment grade issuers (see below and Note 6) as well as equity securities of publicly traded companies (see Note 6).

The following tables summarize the Company's investments in available-for-sale debt securities:



	Amortized		Unrealized					Fair
As of September 30, 2018	Cost Basis		Gains		Losses			Value
Available-for-sale debt securities:
Corporate bonds	$	2,562,051	$	2,316	$	(18,124	)	$	2,546,243
U.S. government and government agency obligations	112,046		25		(1,523		)	110,548
Municipal bonds	2,068		—		(5		)	2,063
Commercial paper	109,412		1		—			109,413
Certificates of deposit	65,940		—		—			65,940
	$	2,851,517	$	2,342	$	(19,652	)	$	2,834,207

As of December 31, 2017
Available-for-sale debt securities:
Corporate bonds	$	1,717,976	$	2,176	$	(7,672	)	$	1,712,480
U.S. government and government agency obligations	186,699		34		(1,241		)	185,492
Municipal bonds	4,600		—		(13		)	4,587
Commercial paper	106,973		—		—			106,973
Certificates of deposit	11,024		—		—			11,024
	$	2,027,272	$	2,210	$	(8,926	)	$	2,020,556

The Company classifies its investments in available-for-sale debt securities based on their contractual maturity dates. The available-for-sale debt securities listed as of September 30, 2018 mature at various dates through March 2023. The fair values of available-for-sale debt security investments by contractual maturity consist of the following:



	September 30, 2018		December 31, 2017
Maturities within one year	$	1,104,309	$	593,783
Maturities after one year through five years	1,729,898		1,426,773
	$	2,834,207	$	2,020,556

The following table shows the fair value of the Company's available-for-sale debt securities that have unrealized losses and that are deemed to be only temporarily impaired, aggregated by investment category and length of time that the individual securities have been in a continuous unrealized loss position.



	Less than 12 Months					12 Months or Greater					Total
As of September 30, 2018	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate bonds	$	1,417,464	$	(10,946	)	$	406,594	$	(7,178	)	$	1,824,058	$	(18,124	)
U.S. government and government agency obligations	7,826		(202		)	95,690		(1,321		)	103,516		(1,523		)
Municipal bonds	—		—			998		(5		)	998		(5		)
	$	1,425,290	$	(11,148	)	$	503,282	$	(8,504	)	$	1,928,572	$	(19,652	)

As of December 31, 2017
Corporate bonds	$	930,970	$	(4,924	)	$	256,750	$	(2,748	)	$	1,187,720	$	(7,672	)
U.S. government and government agency obligations	110,532		(409		)	67,921		(832		)	178,453		(1,241		)
Municipal bonds	2,582		(10		)	2,005		(3		)	4,587		(13		)
	$	1,044,084	$	(5,343	)	$	326,676	$	(3,583	)	$	1,370,760	$	(8,926	)

Realized gains and losses on sales of marketable securities were not material for the three and nine months ended September 30, 2018. There were no realized losses on sales of marketable securities, and realized gains were not material, for the three and nine months ended September 30, 2017.

With respect to marketable securities, for the three and nine months ended September 30, 2018 and 2017, amounts reclassified from Accumulated other comprehensive (loss) income into Other income (expense), net were related to realized gains and losses on sales. The Company adopted ASU 2016-01 (see Note 1) during the first quarter of 2018; as a result, there were $4.9 million of net unrealized losses and $21.0 million of net unrealized gains on equity securities recognized in Other income (expense), net for the three and nine months ended September 30, 2018, respectively. For the three and nine months ended September 30, 2017, there were $27.7 million and $38.9 million, respectively, of net unrealized gains on equity securities that were recorded in Other comprehensive (loss) income.

Fair Value Measurements

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Fair Value Measurements

The Company's assets that are measured at fair value on a recurring basis consist of the following:



			Fair Value Measurements at Reporting Date Using
As of September 30, 2018	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Available-for-sale debt securities:
Corporate bonds	$	2,546,243	—		$	2,546,243
U.S. government and government agency obligations	110,548		—		110,548
Municipal bonds	2,063		—		2,063
Commercial paper	109,413		—		109,413
Certificates of deposit	65,940		—		65,940
Equity securities (unrestricted)	90,445		$	90,445	—
Equity securities (restricted)	53,226		—		53,226
	$	2,977,878	$	90,445	$	2,887,433

As of December 31, 2017
Available-for-sale debt securities:
Corporate bonds	$	1,712,480	—		$	1,712,480
U.S. government and government agency obligations	185,492		—		185,492
Municipal bonds	4,587		—		4,587
Commercial paper	106,973		—		106,973
Certificates of deposit	11,024		—		11,024
Equity securities (unrestricted)	62,785		$	62,785	—
	$	2,083,341	$	62,785	$	2,020,556

Marketable securities included in Level 2 are valued using quoted market prices for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, or model-based valuations in which significant inputs used are observable. The Company considers market liquidity in determining the fair value for these securities. The Company did not record any charges for other-than-temporary impairment of its Level 2 marketable securities during the three and nine months ended September 30, 2018 and 2017.

The Company held restricted equity securities as of September 30, 2018, consisting of the Company's investment in bluebird bio., Inc. common stock, which are subject to transfer restrictions until August 2020.

The fair value of interest rate swap and interest rate cap contracts, which were recorded within Other noncurrent assets, was not material as of September 30, 2018 and December 31, 2017 (see Note 8). The fair value of these contracts was determined based on Level 2 inputs, using significant inputs that are observable either directly or indirectly, including London Interbank Offered Rate ("LIBOR") and interest rate swap rates.

As of September 30, 2018 and December 31, 2017, the Company had $45.5 million and $37.5 million, respectively, in equity investments that do not have a readily determinable fair value. These investments are recorded at cost within Other noncurrent assets.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Inventories

9 Months Ended

Sep. 30, 2018

Inventory Disclosure [Abstract]

Inventories

Inventories consist of the following:



	September 30,		December 31,
	2018		2017
Raw materials	$	216,671	$	190,045
Work-in-process	435,671		302,042
Finished goods	28,397		21,791
Deferred costs	358,940		212,260
	$	1,039,679	$	726,138

Deferred costs represent the costs of product manufactured and shipped to the Company's collaborators for which recognition of revenue has been deferred.

Derivative Instruments and Hedging Activities

9 Months Ended

Sep. 30, 2018

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative Instruments and Hedging Activities

The Company is exposed to market fluctuations in interest rates, including those in connection with its March 2017 lease of laboratory and office facilities in Tarrytown, New York. Commencing in the second quarter of 2017, the Company entered into interest rate swap and interest rate cap agreements to manage a portion of such interest rate risk; no new agreements of this nature were entered into during the nine months ended September 30, 2018. All of the Company's derivative instruments are utilized for risk management purposes, and are not used for trading or speculative purposes.

The Company's derivative instruments are designated as cash flow hedges for accounting purposes. Since the specific terms of the derivative instruments match those of the item being hedged, the derivative instruments are deemed to be highly effective in offsetting the changes in cash flows of the hedged item. As such, changes in the fair value of these derivatives are recorded in accumulated other comprehensive income (loss) until the underlying transaction affects earnings, and are then reclassified to earnings in the same account as the hedged transaction. The Company would record any gain or loss related to the ineffectiveness directly to earnings.

The Company assesses, both at inception and on an ongoing basis, whether derivatives used continue to be highly effective in offsetting changes in cash flows of the hedged items. The Company does not exclude any portion of the cash flow hedge contracts from the assessment of hedge effectiveness. If and when a derivative is no longer expected to be highly effective, hedge accounting would be discontinued.

The following table summarizes the notional amounts of the Company's outstanding interest rate swap and cap agreements:



	September 30,		December 31,
	2018		2017
Interest rate swap contracts	$	75,000	$	75,000
Interest rate cap contracts	$	75,000	$	75,000

As it relates to cash flow hedges, for the three and nine months ended September 30, 2018 and 2017, amounts of gains and losses recognized in Other comprehensive income (loss), and amounts reclassified from Accumulated other comprehensive (loss) income into Interest expense were not material. As of September 30, 2018, the amounts expected to be reclassified out of Accumulated other comprehensive income into Interest expense over the next 12 months are not expected to be material. There was no ineffective portion of the derivative instruments for the three and nine months ended September 30, 2018 and 2017.

Income Taxes	9 Months Ended
Income Taxes	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company is subject to U.S. federal, state, and foreign income taxes. The Company's effective tax rate was 6.5% and 31.3% for the three months ended September 30, 2018 and 2017, respectively, and 13.5% and 32.7% for the nine months ended September 30, 2018 and 2017, respectively. On December 22, 2017, the bill known as the "Tax Cuts and Jobs Act" (the "Act") was signed into law. The Act, which became effective with respect to most of its provisions as of January 1, 2018, significantly revised U.S. corporate income tax laws by, among other things, reducing the U.S. federal corporate income tax rate from 35% to 21%, changing the taxation of foreign earnings (including taxation of certain global intangible low-taxed income ("GILTI")), allowing for a foreign-derived intangible income deduction and immediate expensing for qualified assets, repealing the deduction for domestic manufacturing, and imposing further limitations on the deductibility of executive compensation. As a result of the Act being signed into law, we recognized a provisional charge of $326.2 million in the fourth quarter of 2017 related to the re-measurement of the Company's U.S. net deferred tax assets at the lower enacted corporate tax rate. The provisional charge recorded in the fourth quarter of 2017 is an estimate, and the measurement of deferred tax assets is subject to further analysis, such as developing interpretations and clarifications of the provisions of the Act. During the third quarter of 2018, we recorded an income tax benefit of $11.9 million as an adjustment to the provisional amount recorded as of December 31, 2017. Additional changes to this estimate may occur during the fourth quarter of 2018. In addition, we have not yet elected an accounting method regarding whether to record deferred tax assets and liabilities for expected amounts of GILTI inclusions or whether to treat such amounts as a period cost. The Company's effective tax rate for the three and nine months ended September 30, 2018 was positively impacted, compared to the U.S. federal statutory rate, primarily by the tax benefit associated with tax planning in connection with the Act, the federal tax credit for research activities, and, to a lesser extent, stock-based compensation and income earned in foreign jurisdictions with tax rates lower than the U.S. federal statutory rate. The Company's effective tax rate for the three and nine months ended September 30, 2017 was positively impacted, compared to the U.S. federal statutory rate, by the tax benefit associated with stock-based compensation, the domestic manufacturing deduction, and the federal tax credit for research activities, offset by losses incurred in foreign jurisdictions with rates lower than the U.S. federal statutory rate and the non-tax deductible Branded Prescription Drug Fee. Income tax provisions recorded in the Statement of Comprehensive Income for the three and nine months ended September 30, 2018 and 2017 were not material.

Statement of Cash Flows

9 Months Ended

Sep. 30, 2018

Supplemental Cash Flow Information [Abstract]

Statement of Cash Flows

The Company adopted ASU 2016-18, Statement of Cash Flows - Restricted Cash, during the first quarter of 2018, and the standard has been retrospectively applied to all periods presented. The following provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Consolidated Balance Sheet to the total of the same such amounts shown in the Condensed Consolidated Statement of Cash Flows:



	September 30,		September 30,
	2018		2017
Cash and cash equivalents	$	1,087,843	$	792,065
Restricted cash included in Other noncurrent assets	12,500		12,500
Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statement of Cash Flows	$	1,100,343	$	804,565

Restricted cash consists of amounts held by financial institutions pursuant to contractual arrangements.

Supplemental disclosure of non-cash investing and financing activities

Included in accounts payable, accrued expenses, and other liabilities as of September 30, 2018 and December 31, 2017 were $40.5 million and $41.8 million, respectively, of accrued capital expenditures. Included in accounts payable, accrued expenses, and other liabilities as of September 30, 2017 and December 31, 2016 were $24.5 million and $28.2 million, respectively, of accrued capital expenditures.

As described in Note 3, during the nine months ended September 30, 2018, we purchased (by issuing a credit towards the amount owed by Sanofi) 215,387 shares of our Common Stock from Sanofi to satisfy Sanofi's funding obligation related to Libtayo development costs, and recorded the cost of the shares received, or $75.8 million, as Treasury Stock.

The Company recognized an additional capital lease obligation of $201.2 million in connection with the Company's lease of additional premises at its Tarrytown, New York facility during the nine months ended September 30, 2017.

Legal Matters	9 Months Ended
Legal Matters	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Legal Matters	Legal Matters From time to time, the Company is a party to legal proceedings in the course of the Company's business. Costs associated with the Company's involvement in legal proceedings are expensed as incurred. The outcome of any such proceedings, regardless of the merits, is inherently uncertain. The Company recognizes accruals for loss contingencies associated with such proceedings when it is probable that a liability will be incurred and the amount of loss can be reasonably estimated. Unless otherwise noted below, the Company is unable to predict the outcome, or estimate a range of possible loss or possible gain, of the respective proceedings. If the Company were unable to prevail in any such proceedings, its consolidated financial position, results of operations, and future cash flows may be materially impacted. Proceedings Relating to '287 Patent, '163 Patent, and '018 Patent The Company is a party to patent infringement litigation initiated by the Company involving its European Patent No. 1,360,287 (the "'287 Patent"), its European Patent No. 2,264,163 (the "'163 Patent"), and its U.S. Patent No. 8,502,018 (the "'018 Patent"). Each of these patents concerns genetically engineered mice capable of producing chimeric antibodies that are part human and part mouse. Chimeric antibody sequences can be used to produce high-affinity fully human monoclonal antibodies. In these proceedings, the Company claims infringement of several claims of the '287 Patent, the '163 Patent, and the '018 Patent (as applicable), and seeks, among other types of relief, an injunction and an account of profits in connection with the defendants' infringing acts, which may include, among other things, the making, use, keeping, sale, or offer for sale of genetically engineered mice (or certain cells from which they are derived) that infringe one or more claims of the '287 Patent, the '163 Patent, and the '018 Patent (as applicable). On September 25, 2013, the Company commenced patent infringement litigation against Kymab Ltd in the English High Court of Justice, Chancery Division, Patents Court, in London, asserting the '287 Patent and '163 Patent. A trial to adjudicate the claims of infringement and counterclaims of invalidity of the '287 Patent and the '163 Patent was held from November 16, 2015 through December 8, 2015. On February 1, 2016, the court issued a final judgment, finding that the asserted claims of the '287 and '163 Patents are novel, not obvious, and infringed by Kymab's genetically engineered mice. However, the court invalidated the '287 and '163 Patents on the ground of insufficiency. The hearing for the Company's appeal and Kymab's cross-appeal was held on October 17–20, 2017. On March 28, 2018, the Court of Appeal (Civil Division of England and Wales) reversed the English High Court's decision and held that the '287 Patent and '163 Patent are both valid and infringed by Kymab. On June 5, 2018, the Court of Appeal issued a final order, which enjoins Kymab from infringing the '287 Patent and '163 Patent (subject to certain exceptions) and requires Kymab to destroy or deliver to a third party all products and antibodies and cells engineered to produce antibodies which infringe the '287 Patent and '163 Patent (subject to certain exceptions). The provisions of the final order are stayed pending final determination of Kymab's application for permission to appeal to the Supreme Court of the United Kingdom and, if permission is granted, Kymab's appeal. The Company has also been awarded a portion of the legal fees incurred by it in connection with the proceedings in the English High Court of Justice and the Court of Appeal described above. On March 11, 2014, the Company commenced '287 Patent infringement litigation and '018 Patent infringement litigation against Merus N.V., a company based in Utrecht, The Netherlands, in the District Court of The Hague (currently stayed by agreement of the parties) and the United States District Court for the Southern District of New York, respectively. On November 21, 2014, the United States District Court for the Southern District of New York issued its Opinion and Order on Claim Construction in the '018 Patent infringement litigation, in which it held the '018 Patent invalid and not infringed. On November 2, 2015, the United States District Court for the Southern District of New York issued an opinion and order finding that the '018 Patent was procured by inequitable conduct, thus rendering it unenforceable. On July 27, 2017, the United States Court of Appeals for the Federal Circuit (the "Federal Circuit") affirmed the District Court's decision regarding inequitable conduct without deciding the issues of validity and infringement; and, on December 26, 2017, the Federal Circuit denied the Company's petition for panel rehearing and rehearing en banc. On October 1, 2018, the United States Supreme Court denied the Company's petition for a writ of certiorari. On July 8 and July 13, 2016, notices of opposition against the '163 Patent were filed in the European Patent Office (the "EPO") by Merus N.V. and Kymab and Novo Nordisk A/S, respectively. The notices assert, as applicable, lack of novelty, lack of inventive step, and insufficiency. The Company's response to the oppositions was filed on December 30, 2016. Following an oral hearing before the Opposition Division of the EPO on February 5–7, 2018, the Opposition Division upheld the '163 Patent without amendments. Kymab, Merus, and Novo Nordisk each filed a notice of appeal of the Opposition Division's decision on February 9, 2018, May 25, 2018, and June 26, 2018, respectively. With respect to the '018 Patent infringement litigation against Merus N.V., on June 25, 2018, the United States District Court for the Southern District of New York granted Merus's motion for attorneys' fees and costs in the amount of $10.5 million, plus pre- and post-judgment interest. On July 25, 2018, the Company filed a notice of appeal with the Federal Circuit. If the Company is ultimately required to pay such amounts, this payment is not expected to have a material impact on the Company's financial statements. Proceedings Relating to Praluent (alirocumab) Injection As described in greater detail below, the Company is currently a party to patent infringement actions initiated by Amgen Inc. against the Company and Sanofi (and/or the Company's and Sanofi's respective affiliated entities) in a number of jurisdictions relating to Praluent, which the Company is jointly developing and commercializing with Sanofi. In the United States, Amgen has asserted a number of U.S. patents, which were subsequently narrowed to U.S. Patent Nos. 8,829,165 (the "'165 Patent") and 8,859,741 (the "'741 Patent"), and seeks a permanent injunction to prevent the Company and the Sanofi defendants from commercial manufacturing, using, offering to sell, or selling within the United States (as well as importing into the United States) (collectively, "Commercializing") Praluent. Amgen also seeks a judgment of patent infringement of the asserted patents, monetary damages (together with interest), costs and expenses of the lawsuits, and attorneys' fees. A jury trial in this litigation was held in the United States District Court for the District of Delaware (the "District Court") from March 8 to March 16, 2016. During the course of the trial, the District Court ruled as a matter of law in favor of Amgen that the asserted patent claims were not obvious, and in favor of the Company and the Sanofi defendants that there was no willful infringement of the asserted patent claims by the Company or the Sanofi defendants. On March 16, 2016, the jury returned a verdict in favor of Amgen, finding that the asserted claims of the '165 and '741 Patents were not invalid based on either a lack of written description or a lack of enablement. On January 3, 2017, the District Court issued a final opinion and judgment, denying the Company and the Sanofi defendants' motions for new trial and judgment as a matter of law. The District Court also denied as moot Amgen's motion to strike the Company and the Sanofi defendants' request to obtain a judgment as a matter of law, which allowed the Federal Circuit to address the Company and the Sanofi defendants' patent invalidity arguments on appeal. On January 12, 2017, the Company and the Sanofi defendants filed a notice of appeal with the Federal Circuit. On April 19, 2017, the District Court granted Amgen's motion to amend the judgment on an accounting of supplemental damages and enhancement of such damages if deemed appropriate, but deferred the order until after the Federal Circuit issued a decision on the appeal. Oral argument on the appeal was held on June 6, 2017. On October 5, 2017, the Federal Circuit reversed in part the District Court's decision, remanded for a new trial on the issues of written description and enablement, and, as discussed below, vacated the District Court's permanent injunction. In addition, it affirmed the District Court's ruling that Amgen's patents were not obvious. The Federal Circuit further concluded the Company and the Sanofi defendants were not entitled to judgment as a matter of law on the issues of written description and enablement on this record. On February 23, 2018, the Federal Circuit denied Amgen's petition for rehearing en banc, and on March 2, 2018 the Federal Circuit issued a mandate to transfer jurisdiction of the case back to the District Court. On July 23, 2018, Amgen filed a petition for a writ of certiorari with the United States Supreme Court. Oral argument on the parties' motions for summary judgment and the Company and the Sanofi defendants' motion for judgment on the pleadings regarding Amgen's willful infringement claim is scheduled for January 3, 2019. A new jury trial is currently scheduled to begin on February 19, 2019. On January 5, 2017, the District Court granted a permanent injunction prohibiting Regeneron and the Sanofi defendants from Commercializing Praluent in the United States but subsequently delayed its imposition until February 21, 2017. The Federal Circuit stayed the injunction pending appeal on February 8, 2017 and vacated it on October 5, 2017. On July 25, 2016, Amgen filed a lawsuit against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi-Synthelabo Limited, Aventis Pharma Limited, Sanofi Winthrop Industrie S.A., and Sanofi-Aventis Deutschland GmbH in the English High Court of Justice, Chancery Division, Patents Court, in London, seeking a declaration of infringement of Amgen's European Patent No. 2,215,124 (the "'124 Patent"), which pertains to PCSK9 monoclonal antibodies, by Praluent. The lawsuit also seeks a permanent injunction, damages, an accounting of profits, and costs and interest. On February 8, 2017, the court temporarily stayed this litigation on terms mutually agreed by the parties. Also on July 25, 2016, Amgen filed a lawsuit for infringement of the '124 Patent against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi Winthrop Industrie S.A., and Sanofi-Aventis Deutschland GmbH in the Regional Court of Düsseldorf, Germany (the "Düsseldorf Regional Court"), seeking a permanent injunction, an accounting of marketing activities, a recall of Praluent and its removal from distribution channels, and damages. On November 14, 2017, the Düsseldorf Regional Court issued a decision staying the infringement proceedings until a decision of the Opposition Division of the EPO concerning the pending opposition filed by the Company, Sanofi, and several other opponents against the '124 Patent (as discussed below). Following Amgen's request to reopen the proceedings in light of the issuance of the Preliminary Opinion (as defined below), the Düsseldorf Regional Court held an oral hearing on September 11, 2018 and ruled that the infringement proceedings continue to be stayed. The Düsseldorf Regional Court has also scheduled December 11, 2018 as the date for issuing a decision on Amgen's request for an injunction. On July 12, 2018, Sanofi-Aventis Deutschland GmbH, Sanofi-Aventis Groupe S.A., and Sanofi Winthrop Industrie S.A. filed an action in the Federal Patents Court (the "FPC") in Munich, Germany, seeking a compulsory license from Amgen based on the '124 Patent for the continued commercializing of Praluent in Germany. This compulsory license action included a request for a provisional compulsory license. The FPC held an oral hearing on September 6, 2018 in the provisional compulsory license proceedings and denied Sanofi's request for the provisional compulsory license. The compulsory license proceedings are continuing. On September 26, 2016, Amgen filed a lawsuit for infringement of the '124 Patent in the Tribunal de grande instance in Paris, France against Regeneron, Sanofi-Aventis Groupe S.A., Sanofi Winthrop Industrie, and Sanofi Chimie (subsequently added as a defendant). Amgen is seeking the prohibition of allegedly infringing activities with a €10,000 penalty per drug unit of Praluent produced in violation of the court order sought by Amgen; an appointment of an expert for the assessment of damages; disclosure of technical (including supply-chain) and accounting information to the expert and the court; provisional damages of €10.0 million (which would be awarded on an interim basis pending final determination); reimbursement of costs; publication of the ruling in three newspapers; and provisional enforcement of the decision to be issued, which would ensure enforcement of the decision (including any provisional damages) pending appeal. Amgen is not seeking a preliminary injunction in this proceeding at this time. On April 10, 2017, the Company and the Sanofi parties filed briefs seeking invalidation of certain of the claims of the '124 Patent, and Amgen filed a response on July 28, 2017. Oral hearing on this infringement lawsuit is currently scheduled for February 12, 2019. The '124 Patent is also subject to opposition proceedings in the EPO seeking to invalidate certain of its claims, which were initiated by Sanofi on February 24, 2016 and, separately, by the Company, Sanofi, and several other opponents on November 24, 2016. On December 13, 2017, the Opposition Division of the EPO issued a preliminary, non-binding opinion (the "Preliminary Opinion") regarding the validity of the '124 Patent, indicating that it currently considers the claims of a new request filed by Amgen in response to the opposition to satisfy the requirements for patentability. The Preliminary Opinion was accompanied by a summons to oral hearing to be held on November 28–30, 2018. On May 19, 2017, Amgen filed a lawsuit for infringement of Amgen's Japanese Patent Nos. 5,906,333 (the "'333 Patent") and 5,705,288 (the "'288 Patent") in the Tokyo District Court Civil Division against Sanofi K.K. Amgen's complaint alleges that manufacturing, selling or otherwise transferring, and offering to sell or otherwise transfer Praluent (alirocumab) in Japan (as well as importing Praluent (alirocumab) into Japan) infringe the '333 and '288 Patents. The complaint further seeks a permanent injunction, disposal of product, and court costs. The Company has not been named as a defendant in this litigation. Proceedings Relating to Dupixent (dupilumab) Injection On March 20, 2017, the Company, Sanofi-Aventis U.S. LLC, and Genzyme Corporation filed a lawsuit against Amgen and Immunex Corporation, a wholly owned subsidiary of Amgen, in the United States District Court for the District of Massachusetts seeking a declaratory judgment that the Company's and the other plaintiffs' Commercializing of Dupixent does not directly or indirectly infringe U.S. Patent No. 8,679,487 (the "'487 Patent") owned by Immunex Corporation relating to antibodies that bind the human interleukin-4 receptor. On May 1, 2017, the Company and the other plaintiffs filed a notice of voluntary dismissal of this action without prejudice. On March 23, 2017, the Company, Sanofi-Aventis U.S. LLC, and Genzyme Corporation initiated an inter partes review ("IPR") in the United States Patent and Trademark Office ("USPTO") seeking a declaration of invalidity of the '487 Patent. On July 28 and 31, 2017, the same parties filed two additional IPR petitions in the USPTO seeking declarations of invalidity of the '487 Patent based on different grounds (the "Additional IPR Petitions"). On October 4, 2017, the Patent Trial and Appeal Board ("PTAB") of the USPTO issued a decision on the first IPR petition and declined to institute an IPR proceeding to review the validity of the '487 Patent. On February 15, 2018, the PTAB issued two decisions instituting the Company's and Sanofi's Additional IPR Petitions on all claims of the '487 Patent for which review had been requested. Oral hearing on the Additional IPR Petitions has been scheduled for November 14, 2018. On April 5, 2017, Immunex Corporation filed a lawsuit against the Company, Sanofi, Sanofi-Aventis U.S. LLC, Genzyme Corporation, and Aventisub LLC in the United States District Court for the Central District of California seeking a judgment of patent infringement of the '487 Patent and a declaratory judgment of infringement of the '487 Patent, in each case by the Company's and the other defendants' Commercializing of Dupixent; monetary damages (together with interest); an order of willful infringement of the '487 Patent, which would allow the court in its discretion to award damages up to three times the amount assessed; costs and expenses of the lawsuit; and attorneys' fees. Immunex is not seeking an injunction in this proceeding at this time. On June 21, 2017, the court denied a motion to dismiss Immunex's complaint previously filed by the Company and the Sanofi parties. On June 28, 2017, the Company and the Sanofi parties filed an answer to Immunex's complaint and counterclaims against Immunex and Amgen (which was amended on October 31, 2017 to, among other things, add an inequitable conduct allegation), and Immunex and Amgen filed an answer to the counterclaims on July 28, 2017. A combined hearing on the construction of certain disputed claim terms of the '487 Patent and the Company and the Sanofi parties' motion for summary judgment on the issue of indefiniteness of the '487 Patent claims was held on July 12, 2018. On August 24, 2018, the court issued an order denying this motion and construed the disputed claim terms as proposed by Amgen. A jury trial has been scheduled to start on July 23, 2019. On September 30, 2016, Sanofi initiated a revocation proceeding in the United Kingdom to invalidate the U.K. counterpart of European Patent No. 2,292,665 (the "'665 Patent"), another patent owned by Immunex relating to antibodies that bind the human interleukin-4 receptor. At the joint request of the parties to the revocation proceeding, the U.K. Patents Court ordered on January 30, 2017 that the revocation action be stayed pending the final determination of the currently pending EPO opposition proceedings initiated by the Company and Sanofi in relation to the '665 Patent. The oral hearing before the EPO on the oppositions occurred on November 20, 2017, at which the claims of the '665 Patent were found invalid and the patent was revoked. A final written decision of revocation of the '665 Patent was issued by the EPO on January 4, 2018. Immunex filed a notice of appeal of the EPO's decision on January 31, 2018. On September 20, 2017 and September 21, 2017, respectively, the Company and Sanofi initiated opposition proceedings in the EPO against Immunex's European Patent No. 2,990,420 (the "'420 Patent"), a divisional patent of the '665 Patent (i.e., a patent that shares the same priority date, disclosure, and patent term of the parent '665 Patent but contains claims to a different invention). An oral hearing before the EPO on the '420 Patent opposition proceedings has been scheduled for February 14–15, 2019. The original patent term of the Immunex patents is set to expire in 2021. Proceedings Relating to EYLEA (aflibercept) Injection and ZALTRAP^® (ziv-aflibercept) Injection for Intravenous Infusion On March 19, 2018, Novartis Vaccines and Diagnostics, Inc., Novartis Pharma AG, and Grifols Worldwide Operations Limited (collectively, the "Novartis Parties") filed a lawsuit against the Company in the United States District Court for the Southern District of New York, seeking a judgment of patent infringement of U.S. Patent No. 5,688,688 (the "'688 Patent") by the Company's manufacture of aflibercept (the active ingredient used in both EYLEA and ZALTRAP); monetary damages (together with interest) for a limited period prior to the '688 Patent expiration; an order of willful infringement of the '688 Patent (dismissed on October 24, 2018); costs and expenses of the lawsuit; and attorneys' fees. The '688 Patent expired on November 18, 2014. The Novartis Parties are not seeking an injunction in these proceedings. Proceedings Relating to Shareholder Derivative Claims On December 30, 2015, an alleged shareholder filed a shareholder derivative complaint in the New York Supreme Court, naming the then current and certain former non-employee members of the Company's board of directors, the Chairman of the board of directors, the Company's Chief Executive Officer, and the Company's Chief Scientific Officer as defendants and Regeneron as a nominal defendant. The complaint asserts that the individual defendants breached their fiduciary duties and were unjustly enriched when they approved and/or received allegedly excessive compensation in 2013 and 2014. The complaint seeks damages in favor of the Company for the alleged breaches of fiduciary duties and unjust enrichment; changes to Regeneron's corporate governance and internal procedures; invalidation of the Regeneron Pharmaceuticals, Inc. 2014 Long-Term Incentive Plan with respect to the individual defendants' compensation and a shareholder vote regarding the individual defendants' equity compensation; equitable relief, including an equitable accounting with disgorgement; and award of the costs of the action, including attorneys' fees. On June 28, 2017, the court dismissed the plaintiff's claims with respect to certain compensation awarded in 2013 but denied the defendants' motion to dismiss the other claims set forth in the complaint. On November 8, 2017, another alleged shareholder filed a second shareholder derivative complaint in the New York Supreme Court, naming the then current and certain former non-employee members of the Company's board of directors, the Chairman of the board of directors, the Company's Chief Executive Officer, the Company's Chief Scientific Officer, and Regeneron as defendants. The complaint asserts that the individual defendants breached their fiduciary duties and were unjustly enriched when they approved and/or received allegedly excessive compensation in 2014, 2015, and 2016. The complaint seeks damages in favor of Regeneron for the alleged breaches of fiduciary duties and unjust enrichment; changes to Regeneron's corporate governance and internal procedures; invalidation of Regeneron's 2014 Long-Term Incentive Plan with respect to the individual defendants' compensation and the imposition of meaningful limits on the amount of equity payable to the individual defendants; a shareholder vote regarding the individual defendants' equity compensation; equitable relief, including an equitable accounting with disgorgement; and award of the costs of the action, including attorneys' fees. On December 4, 2017, the plaintiff in the second action moved to consolidate both actions, to be appointed lead plaintiff, and to have its counsel be appointed lead counsel in the proposed consolidated action. The court heard oral argument on March 7, 2018 and denied the motion. The parties in both the first derivative action and the second derivative action agreed to a schedule for document discovery and the filing of defendants' appeal of the court's June 28, 2017 decision, as well as a stay of all non-document discovery pending a decision on defendants' appeal. On March 19, 2018, the defendants appealed the court's June 28, 2017 decision to the Appellate Division of the Supreme Court, First Department. On April 19, 2018, the Appellate Division granted the second plaintiff's motion to intervene in this appeal. On October 9, 2018, the parties to both derivative actions filed with the court a stipulation of compromise and settlement of both derivative actions. The stipulation requires Regeneron to, among other things, impose specified limitations on certain director compensation for the five years starting in December 2018, implement certain corporate governance measures, and pay the agreed-upon amount of attorneys' fees and expenses. On October 10, 2018, the court entered an order scheduling a hearing for final approval of the settlement to be held on December 3, 2018 and providing for notice to Regeneron shareholders. The settlement remains subject to court approval; if approved, both derivative actions will be dismissed with prejudice. By agreement of the parties, the defendants' appeal of the court's June 28, 2017 decision has been adjourned to the Appellate Division's February 2019 term pending final approval of the settlement. Pursuant to the Company's By-Laws and the New York Business Corporation Law, expenses in connection with the foregoing are being advanced by the Company for the individual defendants. On or about December 15, 2015, the Company received a shareholder litigation demand upon the Company's board of directors made by a purported Regeneron shareholder. On or about November 3, 2017, the Company received a second shareholder litigation demand upon the Company's board of directors made by another purported Regeneron shareholder, which was substantially similar to the December 15, 2015 shareholder litigation demand. The demands asserted that the then current and certain former non-employee members of the board of directors and the Chairman of the board of directors excessively compensated themselves in 2013 and 2014. The demands requested that the board of directors investigate and bring legal action against these directors for breach of fiduciary duty, unjust enrichment, and corporate waste, and implement internal controls and systems designed to prohibit and prevent similar actions in the future. On December 20, 2017, the parties to the shareholder derivative action filed on December 30, 2015 entered into a stipulation with the second demanding shareholder. The stipulation provides that the purported shareholder will intervene as a plaintiff in the action, and that the purported shareholder's litigation demand will be withdrawn and deemed null and void. The stipulation was approved by the court on January 18, 2018. The first shareholder litigation demand has also since been withdrawn. Department of Justice Investigation In January 2017, the Company received a subpoena from the U.S. Attorney's Office for the District of Massachusetts requesting documents relating to its support of 501(c)(3) organizations that provide financial assistance to patients; documents concerning its provision of financial assistance to patients with respect to products sold or developed by Regeneron (including EYLEA, Praluent, ARCALYST, and ZALTRAP); and certain other related documents and communications. The Company is cooperating with this investigation.

Recently Issued Accounting Standards	9 Months Ended
Recently Issued Accounting Standards	Sep. 30, 2018
Accounting Policies [Abstract]
Recently Issued Accounting Standards	Recently Issued Accounting Standards In February 2016, the FASB issued ASU 2016-02, Leases. The new standard requires a lessee to recognize on its balance sheet (for both finance and operating leases) a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term. The amendments are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. We plan to adopt this new standard on January 1, 2019 (the "effective date") and use the effective date as our date of initial application. As such, we will not adjust prior period amounts. Furthermore, we expect to elect the practical expedients upon transition, which permit companies to not reassess lease identification, classification, and initial direct costs under the new standard for leases that commenced prior to the effective date. We are currently evaluating the impact that this guidance will have on our financial statements, including related disclosures. The new standard will result in the Company recording additional assets and corresponding liabilities related to operating leases; however, we do not expect the standard to have a material impact to our Consolidated Balance Sheets. The ultimate impact that the new standard will have will depend on the total amount of the Company's lease commitments as of the adoption date. We are in process of implementing a new lease accounting software system and updating our internal controls and processes.

Recently Issued Accounting Standards (Policies)	9 Months Ended
Recently Issued Accounting Standards (Policies)	Sep. 30, 2018
Accounting Policies [Abstract]
Legal Matters	Costs associated with the Company's involvement in legal proceedings are expensed as incurred.
New Accounting Pronouncements	In February 2016, the FASB issued ASU 2016-02, Leases. The new standard requires a lessee to recognize on its balance sheet (for both finance and operating leases) a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term. The amendments are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. We plan to adopt this new standard on January 1, 2019 (the "effective date") and use the effective date as our date of initial application. As such, we will not adjust prior period amounts. Furthermore, we expect to elect the practical expedients upon transition, which permit companies to not reassess lease identification, classification, and initial direct costs under the new standard for leases that commenced prior to the effective date. We are currently evaluating the impact that this guidance will have on our financial statements, including related disclosures. The new standard will result in the Company recording additional assets and corresponding liabilities related to operating leases; however, we do not expect the standard to have a material impact to our Consolidated Balance Sheets. The ultimate impact that the new standard will have will depend on the total amount of the Company's lease commitments as of the adoption date. We are in process of implementing a new lease accounting software system and updating our internal controls and processes.

Interim Financial Statements (Tables)

9 Months Ended

Sep. 30, 2018

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of New Accounting Pronouncements and Changes in Accounting Principles



	September 30, 2018
Balance Sheet Data	As Reported		Adjustments			Balance Without Adoption of ASC 606
Inventories	$	1,039,679	$	17,518		$	1,057,197
Deferred tax assets	$	562,818	$	(15,027	)	$	547,791
Total assets	$	10,805,613	$	2,491		$	10,808,104
Accrued expenses and other current liabilities	$	781,924	$	(1,175	)	$	780,749
Deferred revenue from Sanofi (current)	$	246,812	$	(60,406	)	$	186,406
Deferred revenue - other (current)	$	216,133	$	(78,611	)	$	137,522
Total current liabilities	$	1,417,230	$	(140,192	)	$	1,277,038
Deferred revenue from Sanofi (noncurrent)	$	421,196	$	(28,078	)	$	393,118
Deferred revenue - other (noncurrent)	$	197,651	$	32,952		$	230,603
Total liabilities	$	2,937,313	$	(135,318	)	$	2,801,995
Retained earnings	$	4,433,904	$	137,809		$	4,571,713
Total stockholders' equity	$	7,868,300	$	137,809		$	8,006,109
Total liabilities and stockholders' equity	$	10,805,613	$	2,491		$	10,808,104



	Three Months Ended September 30, 2018									Nine Months Ended September 30, 2018
Consolidated Statement of Operations Data	As Reported			Adjustments			Balance Without Adoption of ASC 606			As Reported			Adjustments			Balance Without Adoption of ASC 606
Sanofi collaboration revenue	$	256,265		$	12,172		$	268,437		$	683,508		$	(5,159	)	$	678,349
Other revenue	$	117,370		$	24,574		$	141,944		$	314,552		$	(22,615	)	$	291,937
Total revenues	$	1,663,496		$	36,746		$	1,700,242		$	4,783,003		$	(27,774	)	$	4,755,229
Cost of collaboration and contract manufacturing	$	79,552		$	(17,518	)	$	62,034		$	180,918		$	(17,518	)	$	163,400
Income from operations	$	626,923		$	54,264		$	681,187		$	1,816,342		$	(10,256	)	$	1,806,086
Income before income taxes	$	635,861		$	54,264		$	690,125		$	1,877,333		$	(10,256	)	$	1,867,077
Income tax expense	$	(41,206	)	$	(2,663	)	$	(43,869	)	$	(253,286	)	$	4,630		$	(248,656	)
Net income	$	594,655		$	51,601		$	646,256		$	1,624,047		$	(5,626	)	$	1,618,421

Product Sales (Tables)

9 Months Ended

Sep. 30, 2018

Revenues [Abstract]

Schedule of product sales

Net product sales consist of the following:



	Three Months Ended September 30,				Nine Months Ended September 30,
Net Product Sales in the United States	2018		2017		2018		2017
EYLEA^®	$	1,021,782	$	953,279	$	2,997,829	$	2,727,132
ARCALYST^®	3,706		4,088		11,950		12,613
	$	1,025,488	$	957,367	$	3,009,779	$	2,739,745

The collaboration revenue we earned from Sanofi is detailed below:



	Three Months Ended September 30,						Nine Months Ended September 30,
Sanofi Collaboration Revenue	2018			2017			2018			2017
Antibody:
Reimbursement of Regeneron research and development expenses	$	76,150		$	128,539		$	201,026		$	421,056
Reimbursement of Regeneron commercialization-related expenses	103,666			90,339			292,756			251,002
Regeneron's share of losses in connection with commercialization of antibodies	(38,924		)	(98,315		)	(182,595		)	(328,998		)
Other	33,166			41,848			82,150			84,338
Total Antibody	174,058			162,411			393,337			427,398
Immuno-oncology:
Reimbursement of Regeneron research and development expenses	74,797			61,649			225,675			188,408
Reimbursement of Regeneron commercialization-related expenses	3,236			1,115			6,507			1,864
Other	4,174			20,000			57,989			60,000
Total Immuno-oncology	82,207			82,764			290,171			250,272
	$	256,265		$	245,175		$	683,508		$	677,670



	Three Months Ended September 30,				Nine Months Ended September 30,
Bayer EYLEA Collaboration Revenue	2018		2017		2018		2017
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	243,152	$	205,367	$	721,522	$	571,126
Reimbursement of Regeneron EYLEA development expenses	1,676		6,053		8,811		10,833
Other	20,764		15,714		45,321		36,910
	$	265,592	$	227,134	$	775,654	$	618,869

Schedules of Concentration of Risk, by Risk Factor



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Besse Medical, a subsidiary of AmerisourceBergen Corporation	57	%	51	%	56	%	51	%
McKesson Corporation	36	%	29	%	37	%	29	%
Curascript SD Specialty Distribution, a subsidiary of Express Scripts	**		19	%	**		19	%
** Sales to Curascript SD Specialty Distribution represented less than 10% of total gross product revenue during the period.

Sales Related Deductions Activity

The following table summarizes the provisions, and credits/payments, for these sales-related deductions during the nine months ended September 30, 2018 and 2017.



	Rebates, Chargebacks, and Discounts			Distribution- Related Fees			Other Sales- Related Deductions			Total
Balance as of December 31, 2017	$	29,840		$	34,142		$	21,320		$	85,302
Provisions	159,060			155,523			29,730			344,313
Credits/payments	(145,813		)	(150,956		)	(35,756		)	(332,525		)
Balance as of September 30, 2018	$	43,087		$	38,709		$	15,294		$	97,090

Balance as of December 31, 2016	$	12,712		$	29,465		$	3,674		$	45,851
Provisions	121,599			140,860			33,518			295,977
Credits/payments	(108,811		)	(136,272		)	(21,444		)	(266,527		)
Balance as of September 30, 2017	$	25,500		$	34,053		$	15,748		$	75,301

Collaboration Agreements (Tables)

9 Months Ended

Sep. 30, 2018

Revenue from Contract with Customer [Abstract]

Schedule of collaboration revenue

Net product sales consist of the following:



	Three Months Ended September 30,				Nine Months Ended September 30,
Net Product Sales in the United States	2018		2017		2018		2017
EYLEA^®	$	1,021,782	$	953,279	$	2,997,829	$	2,727,132
ARCALYST^®	3,706		4,088		11,950		12,613
	$	1,025,488	$	957,367	$	3,009,779	$	2,739,745

The collaboration revenue we earned from Sanofi is detailed below:



	Three Months Ended September 30,						Nine Months Ended September 30,
Sanofi Collaboration Revenue	2018			2017			2018			2017
Antibody:
Reimbursement of Regeneron research and development expenses	$	76,150		$	128,539		$	201,026		$	421,056
Reimbursement of Regeneron commercialization-related expenses	103,666			90,339			292,756			251,002
Regeneron's share of losses in connection with commercialization of antibodies	(38,924		)	(98,315		)	(182,595		)	(328,998		)
Other	33,166			41,848			82,150			84,338
Total Antibody	174,058			162,411			393,337			427,398
Immuno-oncology:
Reimbursement of Regeneron research and development expenses	74,797			61,649			225,675			188,408
Reimbursement of Regeneron commercialization-related expenses	3,236			1,115			6,507			1,864
Other	4,174			20,000			57,989			60,000
Total Immuno-oncology	82,207			82,764			290,171			250,272
	$	256,265		$	245,175		$	683,508		$	677,670



	Three Months Ended September 30,				Nine Months Ended September 30,
Bayer EYLEA Collaboration Revenue	2018		2017		2018		2017
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	243,152	$	205,367	$	721,522	$	571,126
Reimbursement of Regeneron EYLEA development expenses	1,676		6,053		8,811		10,833
Other	20,764		15,714		45,321		36,910
	$	265,592	$	227,134	$	775,654	$	618,869

Schedule of accounts receivable and deferred revenue information

The following table summarizes accounts receivable and deferred revenue information in connection with the Company's IO Collaboration with Sanofi:



	September 30,		December 31,
	2018		2017
Accounts receivable	$	75,627	$	59,274
Deferred revenue	$	468,484	$	440,000

Significant changes in deferred revenue balances are as follows:



	Nine Months Ended September 30, 2018
Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606	$	93,643
Revenue recognized that was included in deferred revenue at the beginning of the period	$	(65,159	)

The following tables summarize accounts receivable and deferred revenue information in connection with the Teva Collaboration Agreement:



	September 30,		December 31,
	2018		2017
Accounts receivable (recorded within Prepaid expenses and other current assets)	$	87,985	$	71,297
Deferred revenue	$	213,660	$	197,357

Significant changes in deferred revenue balances are as follows:



	Nine Months Ended September 30, 2018
Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606	$	48,216
Increase due to amounts invoiced, excluding amounts recognized as revenue during the period	$	33,774
Revenue recognized that was included in deferred revenue at the beginning of the period	$	(67,771	)

The following table summarizes accounts receivable and deferred revenue information in connection with the Company's EYLEA collaboration with Bayer:



	September 30,		December 31,
	2018		2017
Accounts receivable	$	269,155	$	241,153
Deferred revenue	$	85,504	$	68,734

Significant changes in deferred revenue balances are as follows:



	Nine Months Ended September 30, 2018
Increase due to shipments of commercial supplies to Bayer	$	47,958
Revenue recognized that was included in deferred revenue at the beginning of the period	$	(31,188	)

The following table summarizes accounts receivable and deferred revenue information in connection with the Company's Antibody Collaboration with Sanofi:



	September 30,		December 31,
	2018		2017
Accounts receivable	$	187,704	$	121,001
Deferred revenue	$	199,523	$	117,682

Significant changes in deferred revenue balances are as follows:



	Nine Months Ended September 30, 2018
Increase due to shipments of commercial supplies to Sanofi	$	178,608
Revenue recognized that was included in deferred revenue at the beginning of the period	$	(96,767	)

Net Income Per Share (Tables)

9 Months Ended

Sep. 30, 2018

Earnings Per Share [Abstract]

Basic and Diluted Net Income (Loss) Per Share

The calculations of basic and diluted net income per share are as follows:



	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Net income - basic and diluted	$	594,655	$	388,317	$	1,624,047	$	1,024,992

(Shares in thousands)
Weighted average shares - basic	108,033		106,706		107,828		106,108
Effect of dilutive securities:
Stock options	7,027		9,809		6,999		9,386
Restricted stock	28		513		16		500
Dilutive potential shares	7,055		10,322		7,015		9,886
Weighted average shares - diluted	115,088		117,028		114,843		115,994

Net income per share - basic	$	5.50	$	3.64	$	15.06	$	9.66
Net income per share - diluted	$	5.17	$	3.32	$	14.14	$	8.84

Antidilutive Securities

Shares which have been excluded from diluted per share amounts because their effect would have been antidilutive include the following:



	Three Months Ended September 30,		Nine Months Ended September 30,
(Shares in thousands)	2018	2017	2018	2017
Stock options	14,446	4,515	14,821	8,892
Restricted stock	—	—	57	—

Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Available-for-sale Debt Securities

The following tables summarize the Company's investments in available-for-sale debt securities:



	Amortized		Unrealized					Fair
As of September 30, 2018	Cost Basis		Gains		Losses			Value
Available-for-sale debt securities:
Corporate bonds	$	2,562,051	$	2,316	$	(18,124	)	$	2,546,243
U.S. government and government agency obligations	112,046		25		(1,523		)	110,548
Municipal bonds	2,068		—		(5		)	2,063
Commercial paper	109,412		1		—			109,413
Certificates of deposit	65,940		—		—			65,940
	$	2,851,517	$	2,342	$	(19,652	)	$	2,834,207

As of December 31, 2017
Available-for-sale debt securities:
Corporate bonds	$	1,717,976	$	2,176	$	(7,672	)	$	1,712,480
U.S. government and government agency obligations	186,699		34		(1,241		)	185,492
Municipal bonds	4,600		—		(13		)	4,587
Commercial paper	106,973		—		—			106,973
Certificates of deposit	11,024		—		—			11,024
	$	2,027,272	$	2,210	$	(8,926	)	$	2,020,556

Marketable Securities, Based on Contractual Maturity Dates

The fair values of available-for-sale debt security investments by contractual maturity consist of the following:



	September 30, 2018		December 31, 2017
Maturities within one year	$	1,104,309	$	593,783
Maturities after one year through five years	1,729,898		1,426,773
	$	2,834,207	$	2,020,556

Fair Value and Unrealized Losses of Marketable Securities



	Less than 12 Months					12 Months or Greater					Total
As of September 30, 2018	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Corporate bonds	$	1,417,464	$	(10,946	)	$	406,594	$	(7,178	)	$	1,824,058	$	(18,124	)
U.S. government and government agency obligations	7,826		(202		)	95,690		(1,321		)	103,516		(1,523		)
Municipal bonds	—		—			998		(5		)	998		(5		)
	$	1,425,290	$	(11,148	)	$	503,282	$	(8,504	)	$	1,928,572	$	(19,652	)

As of December 31, 2017
Corporate bonds	$	930,970	$	(4,924	)	$	256,750	$	(2,748	)	$	1,187,720	$	(7,672	)
U.S. government and government agency obligations	110,532		(409		)	67,921		(832		)	178,453		(1,241		)
Municipal bonds	2,582		(10		)	2,005		(3		)	4,587		(13		)
	$	1,044,084	$	(5,343	)	$	326,676	$	(3,583	)	$	1,370,760	$	(8,926	)

Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2018

Fair Value Disclosures [Abstract]

Schedule of assets measured at fair value on a recurring basis

The Company's assets that are measured at fair value on a recurring basis consist of the following:



			Fair Value Measurements at Reporting Date Using
As of September 30, 2018	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Available-for-sale debt securities:
Corporate bonds	$	2,546,243	—		$	2,546,243
U.S. government and government agency obligations	110,548		—		110,548
Municipal bonds	2,063		—		2,063
Commercial paper	109,413		—		109,413
Certificates of deposit	65,940		—		65,940
Equity securities (unrestricted)	90,445		$	90,445	—
Equity securities (restricted)	53,226		—		53,226
	$	2,977,878	$	90,445	$	2,887,433

As of December 31, 2017
Available-for-sale debt securities:
Corporate bonds	$	1,712,480	—		$	1,712,480
U.S. government and government agency obligations	185,492		—		185,492
Municipal bonds	4,587		—		4,587
Commercial paper	106,973		—		106,973
Certificates of deposit	11,024		—		11,024
Equity securities (unrestricted)	62,785		$	62,785	—
	$	2,083,341	$	62,785	$	2,020,556

Inventories (Tables)

9 Months Ended

Sep. 30, 2018

Inventory Disclosure [Abstract]

Schedule of Inventory, Current

Inventories consist of the following:



	September 30,		December 31,
	2018		2017
Raw materials	$	216,671	$	190,045
Work-in-process	435,671		302,042
Finished goods	28,397		21,791
Deferred costs	358,940		212,260
	$	1,039,679	$	726,138

Derivative Instruments and Hedging Activities (Tables)

9 Months Ended

Sep. 30, 2018

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Schedule of Notional Amounts of Outstanding Derivative Positions

The following table summarizes the notional amounts of the Company's outstanding interest rate swap and cap agreements:



	September 30,		December 31,
	2018		2017
Interest rate swap contracts	$	75,000	$	75,000
Interest rate cap contracts	$	75,000	$	75,000

Statement of Cash Flows (Tables)

9 Months Ended

Sep. 30, 2018

Supplemental Cash Flow Information [Abstract]

Restrictions on Cash and Cash Equivalents [Table Text Block]

The following provides a reconciliation of cash, cash equivalents, and restricted cash reported within the Condensed Consolidated Balance Sheet to the total of the same such amounts shown in the Condensed Consolidated Statement of Cash Flows:



	September 30,		September 30,
	2018		2017
Cash and cash equivalents	$	1,087,843	$	792,065
Restricted cash included in Other noncurrent assets	12,500		12,500
Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statement of Cash Flows	$	1,100,343	$	804,565

Interim Financial Statements - Narrative (Details) $ in Millions	Jan. 01, 2018 USD ($)
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on retained earnings, net of tax	$ (143.4)
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue	143.4
Equity Securities \| Unrestricted \| Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect on retained earnings, net of tax	6.6
Reclassification from accumulated other comprehensive income, current period, before tax	$ 6.6

Interim Financial Statements - Schedule of Balance Sheet Data (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories	$ 1,039,679	$ 726,138
Deferred tax assets	562,818	506,291
Total assets	10,805,613	8,764,286
Accrued expenses and other current liabilities	781,924	637,162
Total current liabilities	1,417,230	1,135,483
Total liabilities	2,937,313	2,620,208
Retained earnings	4,433,904	2,946,733
Total stockholders' equity	7,868,300	6,144,078
Total liabilities and stockholders' equity	10,805,613	8,764,286
Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories	1,057,197
Deferred tax assets	547,791
Total assets	10,808,104
Accrued expenses and other current liabilities	780,749
Total current liabilities	1,277,038
Total liabilities	2,801,995
Retained earnings	4,571,713
Total stockholders' equity	8,006,109
Total liabilities and stockholders' equity	10,808,104
Adjustments \| Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories	17,518
Deferred tax assets	(15,027)
Total assets	2,491
Accrued expenses and other current liabilities	(1,175)
Total current liabilities	(140,192)
Total liabilities	(135,318)
Retained earnings	137,809
Total stockholders' equity	137,809
Total liabilities and stockholders' equity	2,491
Sanofi
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	246,812	177,746
Deferred revenue, noncurrent	421,196	379,936
Sanofi \| Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	186,406
Deferred revenue, noncurrent	393,118
Sanofi \| Adjustments \| Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	(60,406)
Deferred revenue, noncurrent	(28,078)
Other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	216,133	142,392
Deferred revenue, noncurrent	197,651	$ 249,263
Other \| Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	137,522
Deferred revenue, noncurrent	230,603
Other \| Adjustments \| Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred revenue, current	(78,611)
Deferred revenue, noncurrent	$ 32,952

Interim Financial Statements - Schedule of Statements of Operations Data (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	$ 1,663,496	$ 1,500,673	$ 4,783,003	$ 4,289,780
Income from operations	626,923	559,926	1,816,342	1,540,780
Income before income taxes	635,861	565,605	1,877,333	1,523,744
Income tax expense	(41,206)	(177,288)	(253,286)	(498,752)
Net income	594,655	388,317	1,624,047	1,024,992
Collaboration and contract manufacturing
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of goods sold	79,552	57,844	180,918	141,547
Balance Without Adoption of ASC 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	1,700,242		4,755,229
Income from operations	681,187		1,806,086
Income before income taxes	690,125		1,867,077
Income tax expense	(43,869)		(248,656)
Net income	646,256		1,618,421
Balance Without Adoption of ASC 606 \| Collaboration and contract manufacturing
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of goods sold	62,034		163,400
Accounting Standards Update 2014-09 \| Adjustments
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	36,746		(27,774)
Income from operations	54,264		(10,256)
Income before income taxes	54,264		(10,256)
Income tax expense	(2,663)		4,630
Net income	51,601		(5,626)
Accounting Standards Update 2014-09 \| Adjustments \| Collaboration and contract manufacturing
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of goods sold	(17,518)		(17,518)
Sanofi \| Product and service, other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	256,265	245,175	683,508	677,670
Sanofi \| Balance Without Adoption of ASC 606 \| Product and service, other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	268,437		678,349
Sanofi \| Accounting Standards Update 2014-09 \| Adjustments \| Product and service, other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	12,172		(5,159)
Other \| Product and service, other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	117,370	$ 61,506	314,552	$ 231,446
Other \| Balance Without Adoption of ASC 606 \| Product and service, other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	141,944		291,937
Other \| Accounting Standards Update 2014-09 \| Adjustments \| Product and service, other
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	$ 24,574		$ (22,615)

Product Sales - Schedule of Net Product Sales (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 1,663,496	$ 1,500,673	$ 4,783,003	$ 4,289,780
Product
Disaggregation of Revenue [Line Items]
Revenues	1,025,488	957,367	3,009,779	2,739,745
UNITED STATES \| EYLEA
Disaggregation of Revenue [Line Items]
Revenues	1,021,782	953,279	2,997,829	2,727,132
UNITED STATES \| ARCALYST
Disaggregation of Revenue [Line Items]
Revenues	3,706	4,088	11,950	12,613
UNITED STATES \| Product
Disaggregation of Revenue [Line Items]
Revenues	$ 1,025,488	$ 957,367	$ 3,009,779	$ 2,739,745

Product Sales - Schedule of Concentration of Risk, by Risk Factor (Details) - Gross Sales Revenue - Customer concentration risk	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Besse Medical, a subsidiary of AmerisourceBergen Corporation
Concentration Risk [Line Items]
Concentration risk, percentage	57.00%	51.00%	56.00%	51.00%
McKesson Corporation
Concentration Risk [Line Items]
Concentration risk, percentage	36.00%	29.00%	37.00%	29.00%
Curascript SD Specialty Distribution, a subsidiary of Express Scripts
Concentration Risk [Line Items]
Concentration risk, percentage		19.00%		19.00%

Product Sales - Schedule of Sales Related Deductions Activity (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 85,302	$ 45,851
Provisions	344,313	295,977
Credits/payments	(332,525)	(266,527)
Ending Balance	97,090	75,301
Rebates, Chargebacks, and Discounts
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	29,840	12,712
Provisions	159,060	121,599
Credits/payments	(145,813)	(108,811)
Ending Balance	43,087	25,500
Distribution- Related Fees
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	34,142	29,465
Provisions	155,523	140,860
Credits/payments	(150,956)	(136,272)
Ending Balance	38,709	34,053
Other Sales- Related Deductions
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	21,320	3,674
Provisions	29,730	33,518
Credits/payments	(35,756)	(21,444)
Ending Balance	$ 15,294	$ 15,748

Collaboration Agreements - Schedule of Collaboration Revenue Earned From Sanofi (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 1,663,496	$ 1,500,673	$ 4,783,003	$ 4,289,780
Product and service, other \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	174,058	162,411	393,337	427,398
Product and service, other \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	82,207	82,764	290,171	250,272
Product and service, other \| Sanofi
Disaggregation of Revenue [Line Items]
Revenues	256,265	245,175	683,508	677,670
Reimbursement of Regeneron research and development expenses \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	76,150	128,539	201,026	421,056
Reimbursement of Regeneron research and development expenses \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	74,797	61,649	225,675	188,408
Reimbursement of Regeneron commercialization-related expenses \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	103,666	90,339	292,756	251,002
Reimbursement of Regeneron commercialization-related expenses \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	3,236	1,115	6,507	1,864
Regeneron's share of losses in connection with commercialization of antibodies \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	(38,924)	(98,315)	(182,595)	(328,998)
Other \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	33,166	41,848	82,150	84,338
Other \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	$ 4,174	$ 20,000	$ 57,989	$ 60,000

Collaboration Agreements - Sanofi, Antibodies Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Research and development	$ 556,972	$ 529,749	$ 1,584,847	$ 1,547,159
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Annual funding maximum of research activities per amended agreement					$ 130,000
Percentage of Trial Costs borne by collaborating party			80.00%
Percentage of Trial Costs borne by entity			20.00%
Treasury stock, shares acquired	10,766
Cost of Treasury stock shares received	$ 4,400
Maximum amount of sales milestone payments if total sales achieve specific levels			$ 250,000
Levels of twelve month sales at which sales milestone payments would be received			$ 1,000,000
Period for achieving sales target for milestone payment, rolling basis			12 months
Praluent, Kevzara, and Dupixent \| Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Research and development	$ 13,400	$ 22,600	$ 37,200	$ 68,200

Collaboration Agreements - Schedule of Accounts Receivable and Deferred Revenue Information, Antibody Collaboration (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 269,271	$ 193,684
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Accounts receivable	187,704	121,001
Deferred revenue	$ 199,523	$ 117,682

Collaboration Agreements - Schedule of Significant Changes in Deferred Revenue Balances, Antibody Collaboration (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Increase (decrease) in deferred revenue	$ (29,462)	$ (59,116)
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Increase (decrease) in deferred revenue	178,608
Revenue recognized that was included in deferred revenue at the beginning of the period	$ (96,767)

Collaboration Agreements - Sanofi, Immuno-Oncology Narrative (Details) - Sanofi Collaboration Agreement, Immuno-oncology - USD ($) $ in Millions	1 Months Ended		3 Months Ended		9 Months Ended	12 Months Ended
	Aug. 31, 2018	Jul. 31, 2015	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2018	Dec. 31, 2015
Disaggregation of Revenue [Line Items]
Maximum shares the collaborator could sell (in shares)			1,400,000		1,400,000
Treasury stock, shares acquired			93,786	121,601	215,387
Cost of Treasury stock shares received			$ 38.1	$ 37.6	$ 75.8
Maximum amount of sales milestone payments if total sales achieve specific levels		$ 375.0
Remaining performance obligation			1,562.9		1,562.9
Libtayo
Disaggregation of Revenue [Line Items]
Up-front payment received	$ 20.0
IO Discovery Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received		$ 265.0
License agreement term		5 years
Additional years to extend the agreement		3 years
IO Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received						$ 640.0
IO License and Collaboration Agreement
Disaggregation of Revenue [Line Items]
Up-front payment received		$ 375.0
Maximum amount of shared development costs			1,640.0		1,640.0
Increase amount of shared development costs			$ 990.0		$ 990.0
IO License and Collaboration Agreement \| PD-1
Disaggregation of Revenue [Line Items]
Levels of twelve month sales at which sales milestone payments would be received		$ 2,000.0
Period for achieving sales target for milestone payment, rolling basis		12 months
Through December 31, 2023 \| Libtayo
Disaggregation of Revenue [Line Items]
Percentage of royalties to be paid	8.00%
January 1, 2024 Through December 31, 2026 \| Libtayo
Disaggregation of Revenue [Line Items]
Percentage of royalties to be paid	2.50%

Collaboration Agreements - Schedule of Accounts Receivable and Deferred Revenue Information, IO Collaboration (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 269,271	$ 193,684
Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Accounts receivable	75,627	59,274
Deferred revenue	$ 468,484	$ 440,000

Collaboration Agreements - Schedule of Significant Changes in Deferred Revenue Balances, IO Collaboration (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606	$ (29,462)	$ (59,116)
Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenue recognized that was included in deferred revenue at the beginning of the period	(65,159)
Accounting Standards Update 2014-09 \| Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606	$ 93,643

Collaboration Agreements - Schedule of Collaboration Revenue Earned From Bayer (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 1,663,496	$ 1,500,673	$ 4,783,003	$ 4,289,780
Bayer \| Product and service, other
Disaggregation of Revenue [Line Items]
Revenues	264,373	236,625	775,164	640,919
Outside United States \| Bayer \| Product and service, other
Disaggregation of Revenue [Line Items]
Revenues	265,592	227,134	775,654	618,869
Outside United States \| Bayer \| Net profit in connection with commercialization
Disaggregation of Revenue [Line Items]
Revenues	243,152	205,367	721,522	571,126
Outside United States \| Bayer \| Reimbursement of Regeneron research and development expenses
Disaggregation of Revenue [Line Items]
Revenues	1,676	6,053	8,811	10,833
Outside United States \| Bayer \| Other
Disaggregation of Revenue [Line Items]
Revenues	$ 20,764	$ 15,714	$ 45,321	$ 36,910

Collaboration Agreements - Bayer Narrative (Details) - Bayer - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2017	Sep. 30, 2018
Ang2 Antibody
Disaggregation of Revenue [Line Items]
Up-front payment received	$ 50.0
Minimum
Disaggregation of Revenue [Line Items]
Revenue based on percentage of annual sales in Japan		33.50%
Maximum
Disaggregation of Revenue [Line Items]
Revenue based on percentage of annual sales in Japan		40.00%

Collaboration Agreements - Schedule of Accounts Receivable and Deferred Revenue Information, Bayer Collaboration (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 267,937	$ 242,014
Bayer
Disaggregation of Revenue [Line Items]
Accounts receivable	269,155	241,153
Deferred revenue	$ 85,504	$ 68,734

Collaboration Agreements - Schedule of Significant Changes in Deferred Revenue Balances, Bayer Collaboration (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Increase (decrease) in deferred revenue	$ (29,462)	$ (59,116)
Bayer
Disaggregation of Revenue [Line Items]
Increase (decrease) in deferred revenue	47,958
Revenue recognized that was included in deferred revenue at the beginning of the period	$ (31,188)

Collaboration Agreements - Teva Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				9 Months Ended
	Sep. 30, 2016	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues		$ 1,663,496		$ 1,500,673		$ 4,783,003	$ 4,289,780
Teva
Disaggregation of Revenue [Line Items]
Up-front payment received	$ 250,000
Revenue recognition, milestone method, revenue recognized		60,000	$ 35,000		$ 25,000
Aggregate future development milestone payments the Company is eligible to receive						340,000
Collaborative arrangement, additional eligible aggregate payments						1,890,000
Revenues		69,200		$ 40,200		196,600	$ 141,000
Remaining performance obligation		$ 520,100				$ 520,100

Collaboration Agreements - Schedule of Accounts Receivable and Deferred Revenue Information, Teva Collaboration (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Accounts receivable (recorded within Prepaid expenses and other current assets)	$ 284,807	$ 224,972
Teva
Disaggregation of Revenue [Line Items]
Accounts receivable (recorded within Prepaid expenses and other current assets)	87,985	71,297
Deferred revenue	$ 213,660	$ 197,357

Collaboration Agreements - Schedule of Significant Changes in Deferred Revenue Balances, Teva Collaboration (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606	$ (29,462)	$ (59,116)
Teva \| Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606	48,216
Increase due to amounts invoiced, excluding amounts recognized as revenue during the period	33,774
Revenue recognized that was included in deferred revenue at the beginning of the period	$ (67,771)

Net Income Per Share - Schedule of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net income - basic and diluted	$ 594,655	$ 388,317	$ 1,624,047	$ 1,024,992
Weighted average shares outstanding - basic (in shares)	108,033	106,706	107,828	106,108
Effect of dilutive securities:
Dilutive potential shares (in shares)	7,055	10,322	7,015	9,886
Weighted average shares - diluted (in shares)	115,088	117,028	114,843	115,994
Net income per share - basic (in dollars per share)	$ 5.50	$ 3.64	$ 15.06	$ 9.66
Net income per share - diluted (in dollars per share)	$ 5.17	$ 3.32	$ 14.14	$ 8.84
Stock options
Effect of dilutive securities:
Effect of dilutive securities (in shares)	7,027	9,809	6,999	9,386
Restricted stock
Effect of dilutive securities:
Effect of dilutive securities (in shares)	28	513	16	500

Net Income Per Share - Schedule of Antidilutive Securities Excluded From Computation (Details) - shares shares in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares (in shares)	14,446	4,515	14,821	8,892
Restricted stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average number of shares (in shares)	0	0	57	0

Marketable Securities - Schedule of Investments in Available For Sale Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	$ 2,851,517	$ 2,027,272
Unrealized Gains	2,342	2,210
Unrealized Losses	(19,652)	(8,926)
Fair Value	2,834,207	2,020,556
Corporate bonds \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	2,562,051	1,717,976
Unrealized Gains	2,316	2,176
Unrealized Losses	(18,124)	(7,672)
Fair Value	2,546,243	1,712,480
U.S. government and government agency obligations \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	112,046	186,699
Unrealized Gains	25	34
Unrealized Losses	(1,523)	(1,241)
Fair Value	110,548	185,492
Municipal bonds \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	2,068	4,600
Unrealized Gains	0	0
Unrealized Losses	(5)	(13)
Fair Value	2,063	4,587
Commercial paper \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	109,412	106,973
Unrealized Gains	1	0
Unrealized Losses	0	0
Fair Value	109,413	106,973
Certificates of deposit \| Unrestricted
Debt Securities, Available-for-sale [Line Items]
Amortized Cost Basis	65,940	11,024
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 65,940	$ 11,024

Marketable Securities - Schedule of Debt Securities Based on Contractual Maturity Dates (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Maturities within one year	$ 1,104,309	$ 593,783
Maturities after one year through five years	1,729,898	1,426,773
Total	$ 2,834,207	$ 2,020,556

Marketable Securities - Schedule of Fair Value and Unrealized Losses of Debt Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	$ 1,425,290	$ 1,044,084
Unrealized Loss - Less than 12 months	(11,148)	(5,343)
Fair Value - 12 Months or Greater	503,282	326,676
Unrealized Loss - 12 Months or Greater	(8,504)	(3,583)
Fair Value - Total	1,928,572	1,370,760
Unrealized Loss - Total	(19,652)	(8,926)
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	1,417,464	930,970
Unrealized Loss - Less than 12 months	(10,946)	(4,924)
Fair Value - 12 Months or Greater	406,594	256,750
Unrealized Loss - 12 Months or Greater	(7,178)	(2,748)
Fair Value - Total	1,824,058	1,187,720
Unrealized Loss - Total	(18,124)	(7,672)
U.S. government and government agency obligations
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	7,826	110,532
Unrealized Loss - Less than 12 months	(202)	(409)
Fair Value - 12 Months or Greater	95,690	67,921
Unrealized Loss - 12 Months or Greater	(1,321)	(832)
Fair Value - Total	103,516	178,453
Unrealized Loss - Total	(1,523)	(1,241)
Municipal bonds
Debt Securities, Available-for-sale [Line Items]
Fair Value - Less than 12 Months	0	2,582
Unrealized Loss - Less than 12 months	0	(10)
Fair Value - 12 Months or Greater	998	2,005
Unrealized Loss - 12 Months or Greater	(5)	(3)
Fair Value - Total	998	4,587
Unrealized Loss - Total	$ (5)	$ (13)

Marketable Securities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Investments, Debt and Equity Securities [Abstract]
Net unrealized gain on securities	$ 4.9	$ 27.7	$ 21.0	$ 38.9

Fair Value Measurements - Schedule of Assets Measured at Fair Value on a Recurring Basis (Details) - Measured on a recurring basis - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale debt securities:
Corporate bonds	$ 0	$ 0
U.S. government and government agency obligations	0	0
Municipal bonds	0	0
Commercial paper	0	0
Certificates of deposit	0	0
Total marketable securities	90,445	62,785
Significant Other Observable Inputs (Level 2)
Available-for-sale debt securities:
Corporate bonds	2,546,243	1,712,480
U.S. government and government agency obligations	110,548	185,492
Municipal bonds	2,063	4,587
Commercial paper	109,413	106,973
Certificates of deposit	65,940	11,024
Total marketable securities	2,887,433	2,020,556
Unrestricted \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale debt securities:
Equity securities	90,445	62,785
Unrestricted \| Significant Other Observable Inputs (Level 2)
Available-for-sale debt securities:
Equity securities	0	0
Restricted \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Available-for-sale debt securities:
Equity securities	0
Restricted \| Significant Other Observable Inputs (Level 2)
Available-for-sale debt securities:
Equity securities	53,226
Estimate of Fair Value Measurement
Available-for-sale debt securities:
Corporate bonds	2,546,243	1,712,480
U.S. government and government agency obligations	110,548	185,492
Municipal bonds	2,063	4,587
Commercial paper	109,413	106,973
Certificates of deposit	65,940	11,024
Total marketable securities	2,977,878	2,083,341
Estimate of Fair Value Measurement \| Unrestricted
Available-for-sale debt securities:
Equity securities	90,445	$ 62,785
Estimate of Fair Value Measurement \| Restricted
Available-for-sale debt securities:
Equity securities	$ 53,226

Fair Value Measurements - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities owned not readily marketable	$ 45,500		$ 45,500		$ 37,500
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other than temporary impairment losses, investments	$ 0	$ 0	$ 0	$ 0

Inventories - Schedule of Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 216,671	$ 190,045
Work-in-process	435,671	302,042
Finished goods	28,397	21,791
Deferred costs	358,940	212,260
Total Inventories	$ 1,039,679	$ 726,138

Derivative Instruments and Hedging Activities - Schedule of Notional Amounts of Outstanding Derivative Positions (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Derivative [Line Items]
Gain (loss) related to ineffective portion of the derivative instruments	$ 0	$ 0	$ 0	$ 0
Interest rate swap contracts
Derivative [Line Items]
Derivative, notional amount	75,000,000		75,000,000		$ 75,000,000
Interest rate cap contracts
Derivative [Line Items]
Derivative, notional amount	$ 75,000,000		$ 75,000,000		$ 75,000,000

Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
Income Taxes - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Effective income tax rate	6.50%		31.30%	13.50%	32.70%
Domestic Tax Authority
Operating Loss Carryforwards [Line Items]
Provisional charge for re-measurement of U.S. deferred tax assets due to US Tax Reform		$ 326.2
Income tax expense (benefit)	$ (11.9)

Statement of Cash Flows - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Supplemental Cash Flow Information [Abstract]
Cash and cash equivalents	$ 1,087,843	$ 812,733	$ 792,065
Restricted cash included in Other noncurrent assets	12,500		12,500
Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statement of Cash Flows	$ 1,100,343	$ 825,233	$ 804,565	$ 547,703

Statement of Cash Flows - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Condensed Cash Flow Statements, Captions [Line Items]
Accrued capital expenditures	$ 40.5		$ 40.5	$ 24.5	$ 41.8	$ 28.2
Capital lease obligations incurred				$ 201.2
Sanofi Collaboration Agreement, Immuno-oncology
Condensed Cash Flow Statements, Captions [Line Items]
Treasury stock, shares acquired	93,786	121,601	215,387
Cost of Treasury stock shares received	$ 38.1	$ 37.6	$ 75.8

Legal Matters - Narrative (Details) $ in Millions	Jun. 25, 2018 USD ($)	Sep. 26, 2016 EUR (€)
Loss Contingency [Abstract]
Attorneys' fees \| $	$ 10.5
Loss contingency, damages sought, per unit produced		€ 10,000
Loss contingency, damages sought, amount		€ 10,000,000