Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Sep. 30, 2016	Oct. 20, 2016
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, 2016
Document Fiscal Year Focus	2016
Document Fiscal Period Focus	Q3
Amendment Flag	false
Common Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		103,558,843
Class A Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,911,456

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 920,359	$ 809,102
Marketable securities	488,032	236,121
Accounts receivable - trade, net	1,332,071	1,152,489
Accounts Receivable from Sanofi	124,107	153,152
Accounts receivable from Bayer	187,694	162,152
Inventories	345,620	238,578
Prepaid expenses and other current assets	103,806	163,501
Total current assets	3,501,689	2,915,095
Marketable securities	777,906	632,162
Property, plant, and equipment, net	1,872,167	1,594,120
Deferred tax assets	655,552	461,945
Other assets	20,705	5,810
Total assets	6,828,019	5,609,132
Current liabilities:
Accounts payable and accrued expenses	714,916	644,112
Deferred revenue from Sanofi, current portion	105,041	101,573
Deferred revenue - other, current portion	137,642	51,914
Other current liabilities	3,586	13,563
Total current liabilities	961,185	811,162
Deferred revenue from Sanofi	529,791	582,664
Deferred Revenue - other	327,868	82,015
Facility lease obligations	382,228	362,919
Other long-term liabilities	135,700	115,535
Total liabilities	2,336,772	1,954,295
Stockholders' equity:
Preferred Stock	0	0
Additional paid-in capital	3,314,982	3,099,526
Retained earnings	1,495,107	852,700
Accumulated other comprehensive (loss) income	(2,899)	8,572
Treasury stock	(316,052)	(306,069)
Total stockholders' equity	4,491,247	3,654,837
Total liabilities and stockholders' equity	6,828,019	5,609,132
Class A Stock
Stockholders' equity:
Common stock	2	2
Common Stock
Stockholders' equity:
Common stock	$ 107	$ 106

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Sep. 30, 2016	Dec. 31, 2015
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, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Treasury Stock, shares outstanding (in shares)	3,761,628	3,642,820
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)	1,911,456	1,913,776
Common Stock, shares outstanding (in shares)	1,911,456	1,913,776
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)	107,311,675	106,378,001

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Revenues:
Net product sales	$ 857,468	$ 737,562	$ 2,475,869	$ 1,939,954
Sanofi collaboration revenue	144,392	224,735	527,500	593,201
Bayer Collaboration Revenue	191,298	157,596	562,786	415,679
Other revenue	26,964	17,529	67,445	56,817
Total revenues	1,220,122	1,137,422	3,633,600	3,005,651
Expenses:
Research and development	543,047	425,924	1,573,089	1,159,367
Selling, general, and administrative	270,045	209,993	851,760	543,572
Cost of goods sold	29,901	67,199	150,090	170,624
Cost of collaboration and contract manufacturing	14,327	41,884	74,923	111,254
Total expenses	857,320	745,000	2,649,862	1,984,817
Income from operations	362,802	392,422	983,738	1,020,834
Other income (expense):
Investment income	3,301	2,140	8,351	3,973
Interest and other expense, net	(222)	(1,273)	(3,801)	(26,999)
Nonoperating Income (Expense)	3,079	867	4,550	(23,026)
Income before income taxes	365,881	393,289	988,288	997,808
Income tax expense	(101,077)	(182,891)	(345,881)	(516,746)
Net income	$ 264,804	$ 210,398	$ 642,407	$ 481,062
Net income per share - basic	$ 2.53	$ 2.04	$ 6.14	$ 4.68
Net income per share - diluted	$ 2.27	$ 1.82	$ 5.51	$ 4.18
Weighted average shares outstanding - basic	104,833	103,348	104,586	102,825
Weighted average shares outstanding - diluted	116,466	115,944	116,567	115,144
Statements of Comprehensive Income
Net income	$ 264,804	$ 210,398	$ 642,407	$ 481,062
Other comprehensive income (loss):
Unrealized loss on marketable securities, net of tax	(8,103)	(11,432)	(11,471)	(44,530)
Comprehensive income	$ 256,701	$ 198,966	$ 630,936	$ 436,532

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 642,407	$ 481,062
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	75,845	51,999
Non-cash compensation expense	405,320	300,657
Other non-cash charges and expenses, net	13,586	34,919
Increase (Decrease) in Deferred Income Taxes	(190,327)	(65,975)
Changes in assets and liabilites
Increase in Sanofi, Bayer, and trade accounts receivable	(176,079)	(462,943)
Increase in Inventories	(99,706)	(66,254)
Decrease (increase) in prepaid expenses and other assets	34,857	(13,223)
Increase in deferred revenue	282,176	624,063
Increase in accounts payable, accrued expenses and other liabilities	107,438	164,652
Total adjustments	453,110	567,895
Net cash provided by operating activities	1,095,517	1,048,957
Cash flows from investing activities:
Purchases of marketable securities	(606,153)	(550,142)
Sales or maturities of marketable securities	192,091	265,995
Capital expenditures	(361,486)	(500,154)
Net cash used in investing activities	(775,548)	(784,301)
Cash flows from financing activities:
Proceeds in connection with facility lease obligations	3,232	26,405
Repayments of convertible senior notes	(12,650)	(146,007)
Payments in connection with deduction of outstanding warrants	(242,117)	(523,487)
Proceeds from issuance of Common Stock	89,777	150,423
Payments in connection with Common Stock tendered for employee tax obligations	(46,954)	(71,673)
Excess tax benefit from stock-based compensation	0	305,551
Net cash used in by financing activities	(208,712)	(258,788)
Net increase in cash and cash equivalents	111,257	5,868
Cash and cash equivalents at beginning of period	809,102	648,719
Cash and cash equivalents at end of period	$ 920,359	$ 654,587

Interim Financial Statements (Notes)	9 Months Ended
Interim Financial Statements (Notes)	Sep. 30, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Interim Financial Statements	Interim Financial Statements The interim Condensed Consolidated Financial Statements of Regeneron Pharmaceuticals, Inc. and its subsidiaries ("Regeneron" or the "Company") 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 periods are not necessarily indicative of the results for the full year. The December 31, 2015 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, 2015. Certain reclassifications have been made to prior period amounts to conform with the current period's presentation.

Net Product Sales (Notes)

9 Months Ended

Sep. 30, 2016

Revenues [Abstract]

Product Sales and Concentration Risk [Text Block]

Product Sales

EYLEA^® net product sales in the United States totaled $853.6 million and $734.4 million for the three months ended September 30, 2016 and 2015, respectively, and $2,465.4 million and $1,930.0 million for the nine months ended September 30, 2016 and 2015, respectively. In addition, ARCALYST^® net product sales totaled $3.9 million and $3.2 million for the three months ended September 30, 2016 and 2015, respectively, and $10.5 million and $9.9 million for the nine months ended September 30, 2016 and 2015, respectively.

Revenue from product sales is recorded net of applicable provisions for rebates and chargebacks, distribution-related fees, and other sales-related deductions. The following table summarizes the provisions, and credits/payments, for these sales-related deductions during the nine months ended September 30, 2016 and 2015.



	Rebates & Chargebacks			Distribution- Related Fees			Other Sales- Related Deductions			Total
Balance as of December 31, 2015	$	6,419		$	48,313		$	517		$	55,249
Provision related to current period sales	63,510			113,755			22,812			200,077
Credits/payments	(62,503		)	(135,483		)	(19,587		)	(217,573		)
Balance as of September 30, 2016	$	7,426		$	26,585		$	3,742		$	37,753

Balance as of December 31, 2014	$	3,083		$	21,166		$	532		$	24,781
Provision related to current period sales	41,290			88,049			6,024			135,363
Credits/payments	(38,011		)	(71,007		)	(6,052		)	(115,070		)
Balance as of September 30, 2015	$	6,362		$	38,208		$	504		$	45,074

Collaboration Agreements (Notes)

9 Months Ended

Sep. 30, 2016

Collaboration Agreement [Abstract]

Collaboration Agreements

a. Sanofi

The collaboration revenue the Company earned from Sanofi is detailed below:



	Three Months Ended September 30,
Sanofi Collaboration Revenue	2016			2015
Antibody:
Reimbursement of Regeneron research and development expenses	$	131,389		$	205,114
Reimbursement of Regeneron commercialization-related expenses	65,703			53,341
Regeneron's share of losses in connection with commercialization of antibodies	(112,001		)	(74,865		)
Other	3,075			2,561
Total Antibody	88,166			186,151
Immuno-oncology:
Reimbursement of Regeneron research and development expenses	36,226			18,584
Other	20,000			20,000
Total Immuno-oncology	56,226			38,584
	$	144,392		$	224,735



	Nine Months Ended September 30,
Sanofi Collaboration Revenue	2016			2015
Antibody:
Reimbursement of Regeneron research and development expenses	$	469,223		$	585,450
Reimbursement of Regeneron commercialization-related expenses	224,862			89,145
Regeneron's share of losses in connection with commercialization of antibodies	(333,530		)	(143,583		)
Other	9,094			7,683
Total Antibody	369,649			538,695
Immuno-oncology:
Reimbursement of Regeneron research and development expenses	97,851			18,584
Other	60,000			20,000
Total Immuno-oncology	157,851			38,584
ZALTRAP^®:
Reimbursement of Regeneron research and development expenses	—			686
Other	—			15,236
Total ZALTRAP	—			15,922
	$	527,500		$	593,201

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 is 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 is obligated to fund up to $130.0 million of the Company's research activities in 2016. Under the License and Collaboration Agreement, agreed-upon worldwide development expenses incurred by both companies are funded by Sanofi, except that 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. During the three months ended September 30, 2016 and 2015, the Company recognized as additional research and development expense $27.9 million and $25.1 million, respectively, and during the nine months ended September 30, 2016 and 2015, the Company recognized as additional research and development expense $80.2 million and $72.6 million, respectively, of antibody development expenses that the Company was obligated to reimburse to Sanofi related to Praluent^®, sarilumab, and, commencing in the first quarter of 2016, Dupixent^® (dupilumab).

Reimbursement of Regeneron commercialization-related expenses represents reimbursement of internal and external costs in connection with preparing to commercialize or commercializing, as applicable, Praluent, sarilumab, and, effective in the first quarter of 2016, Dupixent.

During the nine months ended September 30, 2015, the Company and Sanofi shared commercialization expenses, including those incurred by Sanofi, related to Praluent and sarilumab in accordance with the companies’ License and Collaboration Agreement. In July 2015, the U.S. Food and Drug Administration ("FDA") approved Praluent in the United States and in September 2015, the European Commission granted marketing authorization of Praluent. Therefore, commencing in the third quarter of 2015, the Company also recorded within Sanofi collaboration revenue its share of the Antibody Collaboration's losses in connection with commercialization of Praluent. In addition, effective in the first quarter of 2016, the Company and Sanofi also began sharing pre-launch commercialization expenses related to Dupixent. As such, during the three and nine months ended September 30, 2016, the Company recorded its share of losses in connection with preparing to commercialize or commercializing, as applicable, Praluent, sarilumab, and Dupixent within Sanofi collaboration revenue.

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"). Pursuant to the IO Discovery Agreement, Sanofi will reimburse the Company for up to $150.0 million in 2016 to identify and validate potential immuno-oncology targets and develop therapeutic antibodies against such targets through clinical proof-of-concept. Under the terms of the IO License and Collaboration Agreement, the parties are co-developing the Company's antibody product candidate targeting the receptor known as programmed cell death protein 1, or PD-1 ("REGN2810"). The parties share equally, on an ongoing basis, development expenses for REGN2810.

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 by the Company as deferred revenue, and is being recognized ratably as revenue over the related performance period.

ZALTRAP

In February 2015, the Company and Sanofi entered into an amended and restated ZALTRAP agreement ("Amended ZALTRAP Agreement"). Under the terms of the Amended ZALTRAP Agreement, Sanofi is solely responsible for the development and commercialization of ZALTRAP for cancer indications worldwide. Sanofi bears the cost of all development and commercialization activities and reimburses Regeneron for its costs for any such activities. Sanofi pays the Company a percentage of aggregate net sales of ZALTRAP during each calendar year.

As a result of entering into the Amended ZALTRAP Agreement, in the first quarter of 2015, the Company recognized $14.9 million of collaboration revenue, which was previously recorded as deferred revenue under the ZALTRAP Collaboration Agreement, related to (i) amounts that were previously reimbursed by Sanofi for manufacturing commercial supplies of ZALTRAP since the risk of inventory loss no longer existed, and (ii) the unamortized portion of up-front payments from Sanofi as the Company had no further performance obligations. In addition, during the three months ended September 30, 2016 and 2015, the Company recorded $6.7 million and $9.0 million, respectively, and during the nine months ended September 30, 2016 and 2015, the Company recorded $21.3 million and $32.0 million, respectively, in other revenue primarily related to a percentage of net sales of ZALTRAP and manufacturing ZALTRAP commercial supplies for Sanofi.

b. Bayer

The collaboration revenue the Company earned from Bayer is detailed below:



	Three Months Ended September 30,
Bayer Collaboration Revenue	2016		2015
EYLEA:
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	170,854	$	130,510
Cost-sharing of Regeneron EYLEA development expenses	2,219		1,827
Other	6,077		21,155
Total EYLEA	179,150		153,492
PDGFR-beta antibody:
Cost-sharing of rinucumab/aflibercept (REGN2176-3) development expenses	3,912		1,508
Other	2,603		2,596
Total PDGFR-beta	6,515		4,104
Ang2 antibody:
Cost-sharing of nesvacumab/aflibercept (REGN910-3) development expenses	3,521		—
Other	2,112		—
Total Ang2	5,633		—
	$	191,298	$	157,596



	Nine Months Ended September 30,
Bayer Collaboration Revenue	2016		2015
EYLEA:
Regeneron's net profit in connection with commercialization of EYLEA outside the United States	$	484,181	$	326,567
Sales milestones	—		15,000
Cost-sharing of Regeneron EYLEA development expenses	7,186		6,948
Other	45,924		50,685
Total EYLEA	537,291		399,200
PDGFR-beta antibody:
Cost-sharing of rinucumab/aflibercept (REGN2176-3) development expenses	8,570		8,688
Other	7,836		7,791
Total PDGFR-beta antibody	16,406		16,479
Ang2 antibody:
Cost-sharing of nesvacumab/aflibercept (REGN910-3) development expenses	5,595		—
Other	3,494		—
Total Ang2 antibody	9,089		—
	$	562,786	$	415,679

EYLEA outside the United States

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, all agreed-upon EYLEA development costs incurred by the Company and Bayer are shared equally. In the first quarter of 2015, the Company earned a $15.0 million sales milestone from Bayer upon total aggregate net sales of specific commercial supplies of EYLEA outside the United States exceeding $200 million over a twelve-month period, which was the final milestone payment under the agreement.

PDGFR-beta antibody outside the United States

In 2014, the Company entered into an 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), including in combination with aflibercept, for the treatment of ocular diseases or disorders. In connection with the agreement, Bayer is obligated to pay 25% of global development costs and 50% of development costs exclusively for the territory outside the United States.

Ang2 antibody outside the United States

In March 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), including in combination with aflibercept, for the treatment of ocular diseases or disorders. In connection with the agreement, Bayer made a $50.0 million non-refundable up-front payment to the Company and is obligated to pay 25% of global development costs and 50% of development costs exclusively for the territory outside the United States. The Company is also entitled to receive up to an aggregate of $80.0 million in development milestone payments from Bayer. Bayer will share profits and losses from sales outside the United States equally with the Company, and is responsible for certain royalties payable to Sanofi on sales of the product outside of the United States. Within the United States, the Company has exclusive commercialization rights and will retain all of the profits from sales.

At the inception of the agreement, the Company's significant deliverables consisted of (i) a license to certain rights and intellectual property, (ii) providing research and development services, and (iii) manufacturing clinical supplies. The Company concluded that the license did not have standalone value, as such right was not sold separately by the Company, nor could Bayer receive any benefit from the license without the fulfillment of other ongoing obligations by the Company, including the clinical supply arrangement. Therefore, the deliverables were considered a single unit of accounting. Consequently, the $50.0 million up-front payment was initially recorded as deferred revenue, and will be recognized ratably as revenue over the related performance period.

Unless terminated earlier in accordance with its provisions, the agreement will continue to be in effect until such time as neither party or its respective affiliates or sublicensees is developing or commercializing an Ang2 antibody in the specified field outside of the United States and such discontinuation is acknowledged as permanent by both the Company and Bayer.

c. Mitsubishi Tanabe Pharma

In September 2015, the Company and Mitsubishi Tanabe Pharma Corporation ("MTPC") entered into a collaboration agreement providing MTPC with development and commercial rights to fasinumab, the Company's nerve growth factor antibody in late-stage clinical development, in certain Asian countries. In connection with the agreement, MTPC made a $10.0 million non-refundable up-front payment. In the first quarter of 2016, MTPC made additional payments of $45.0 million and $15.0 million to the Company, which were recorded as deferred revenue and will be recognized ratably as revenue over the same performance period as the up-front payment.

d. 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 the Company's collaboration agreement with MTPC (as described above). In connection with the Teva Collaboration Agreement, Teva made a $250.0 million non-refundable up-front payment in September 2016. The Company will lead global development activities, and the parties will share equally, on an ongoing basis, development costs under a global development plan. In addition, the Company is entitled to receive up to an aggregate of $460.0 million in development milestones and up to an aggregate of $1,890.0 million in contingent payments upon achievement of specified annual net sales amounts. The Company is responsible for the manufacture and supply of fasinumab globally.

Within the United States, the Company will lead commercialization activities, and the parties will share equally in any profits and losses in connection with commercialization of fasinumab. In the territory outside the United States, Teva will lead commercialization activities and the Company will supply product to Teva at a tiered purchase price, which is calculated as a percentage of net sales of the product (subject to adjustment in certain circumstances). Unless terminated earlier in accordance with its provisions, the Teva Collaboration Agreement will continue to be in effect until such time as neither party is developing or commercializing fasinumab.

At the inception of the Teva Collaboration Agreement, the Company's significant deliverables consisted of (i) a license to certain rights and intellectual property, (ii) providing research and development services, and (iii) manufacturing clinical supplies. The Company concluded that the license did not have standalone value, primarily due to the fact that such rights were not sold separately by the Company, nor could Teva receive any benefit from the license without the fulfillment of the other ongoing obligations by the Company, including the clinical supply arrangement. Therefore, the deliverables were considered a single unit of accounting. Consequently, the $250.0 million up-front payment was initially recorded as deferred revenue, and will be recognized ratably as revenue over the related performance period.

e. Intellia Therapeutics

In April 2016, the Company entered into a license and collaboration agreement with Intellia Therapeutics, Inc. to advance CRISPR/Cas gene-editing technology for in vivo therapeutic development. The Company will collaborate with Intellia to conduct research for the discovery, development, and commercialization of new therapies ("Product Collaboration"), in addition to the research and technology development of the CRISPR/Cas platform ("Technology Collaboration"). In connection with the execution of the agreement, the Company made a $75.0 million up-front payment, which was recorded as research and development expense in the second quarter of 2016, and also agreed to purchase Intellia shares contingent upon Intellia consummating its next equity financing. The Company is responsible for costs of developing and commercializing CRISPR/Cas products under the Product Collaboration agreement and is also obligated to pay potential development and sales milestones, and royalties on any future sales of such products resulting from the development and commercialization of CRISPR/Cas products. In addition, under the Technology Collaboration agreement, the Company is responsible for funding certain research and technology development costs.

Under the terms of the Product Collaboration agreement, the parties agreed to a target selection process, whereby the Company may obtain exclusive rights in up to 10 targets to be chosen by the Company during the collaboration term, subject to various adjustments and limitations set forth in the agreement. Additionally, the Company may replace a limited number of targets with substitute targets upon the payment of a replacement fee, in which case rights to the replaced target(s) will revert to Intellia.

The Technology Collaboration term and the period for selecting targets for inclusion under the Product Collaboration both end in 2022, provided that the Company may make a payment to extend the term for an additional two-year period. The Product Collaboration agreement will continue until the date when no royalty or other payment obligations are due, unless earlier terminated in accordance with the terms of the agreement.

Certain targets that either the Company or Intellia select pursuant to the target selection process may be subject to a co-development and co-commercialization arrangement at the Company's option or Intellia's option, as applicable.

In May 2016, Intellia completed an initial public offering ("IPO") of its common stock and thereby triggered the Company's obligation to purchase up to $50.0 million of Intellia common stock in a concurrent private placement. As part of the concurrent private placement, the Company purchased from Intellia at the closing of the IPO 2,777,777 shares of Intellia common stock for an aggregate purchase price of $50.0 million (see Note 5).

f. Adicet Bio

In July 2016, the Company entered into a license and collaboration agreement with Adicet Bio, Inc., a privately held company, to develop next-generation engineered immune-cell therapeutics with fully human chimeric antigen receptors ("CARs") and T-cell receptors ("TCRs") directed to disease-specific cell surface antigens in order to enable the precise engagement and killing of tumor cells. In connection with the execution of the agreement, the Company made a $25.0 million up-front payment to Adicet, which was recorded as research and development expense in the third quarter of 2016, and is obligated to provide Adicet with research funding over the course of a five-year research term.

Under the terms of the agreement, the Company and Adicet will collaborate to identify and validate targets and work together to develop a pipeline of engineered immune-cell therapeutics for selected targets. The Company has the option to obtain development and commercial rights for a certain number of the product candidates developed by the parties, subject to an option payment for each product candidate. If the Company exercises its option on a given product candidate, Adicet then will have an option to participate in the development and commercialization for such product. If Adicet doesn’t exercise its option, Adicet will be entitled to royalties on any future sales of such products by the Company. In addition to developing CARs and TCRs for use in novel immune-cell therapies as part of the collaboration, the Company will have the right to use these CARs and TCRs in its other antibody programs outside of the collaboration.

The Company will also be entitled to royalties on any future sales of products developed and commercialized by Adicet under the agreement for all products for which the Company does not have development and commercial rights.

Net Income Per Share (Notes)

9 Months Ended

Sep. 30, 2016

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,
	2016		2015
Net income - basic	$	264,804	$	210,398
Effect of dilutive securities:
Convertible senior notes - interest expense related to contractual coupon interest rate and amortization of discount and note issuance costs	—		145
Net income - diluted	$	264,804	$	210,543

(Shares in thousands)
Weighted average shares - basic	104,833		103,348
Effect of dilutive securities:
Stock options	10,156		9,632
Restricted stock	479		481
Convertible senior notes	—		308
Warrants	998		2,175
Dilutive potential shares	11,633		12,596
Weighted average shares - diluted	116,466		115,944

Net income per share - basic	$	2.53	$	2.04
Net income per share - diluted	$	2.27	$	1.82



	Nine Months Ended September 30,
	2016		2015
Net income - basic	$	642,407	$	481,062
Effect of dilutive securities:
Convertible senior notes - interest expense related to contractual coupon interest rate and amortization of discount and note issuance costs	397		—
Net income - diluted	$	642,804	$	481,062

(Shares in thousands)
Weighted average shares - basic	104,586		102,825
Effect of dilutive securities:
Stock options	10,340		9,449
Restricted stock	474		475
Convertible senior notes	81		—
Warrants	1,086		2,395
Dilutive potential shares	11,981		12,319
Weighted average shares - diluted	116,567		115,144

Net income per share - basic	$	6.14	$	4.68
Net income per share - diluted	$	5.51	$	4.18

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,
(Shares in thousands)	2016	2015
Stock options	7,687	594
Restricted stock	19	—
Convertible senior notes	3	—



	Nine Months Ended September 30,
(Shares in thousands)	2016	2015
Stock options	7,842	3,388
Restricted stock	19	—
Convertible senior notes	—	1,253

Marketable Securities (Notes)

9 Months Ended

Sep. 30, 2016

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

Marketable securities as of September 30, 2016 and December 31, 2015 consist of both debt securities of investment grade issuers as well as equity securities. The Company also held restricted marketable securities as of September 30, 2016, consisting of the Company's investment in shares of Intellia common stock (see Note 3), which are subject to customary transfer restrictions until November 2016 under a lock-up agreement with the underwriters of Intellia's IPO.

The following tables summarize the Company's investments in marketable securities:



	Amortized		Unrealized					Fair
As of September 30, 2016	Cost Basis		Gains		Losses			Value
Unrestricted
Corporate bonds	$	966,235	$	2,247	$	(561	)	$	967,921
U.S. government and government agency obligations	115,917		219		(40		)	116,096
Municipal bonds	10,205		21		(1		)	10,225
Commercial paper	73,417		2		—			73,419
Certificates of deposit	36,056		—		—			36,056
Equity securities	17,005		8,624		(7,565		)	18,064
	1,218,835		11,113		(8,167		)	1,221,781
Restricted
Equity Securities	50,000		—		(5,843		)	44,157
	$	1,268,835	$	11,113	$	(14,010	)	$	1,265,938

As of December 31, 2015
Unrestricted
Corporate bonds	$	770,092	$	156	$	(2,565	)	$	767,683
U.S. government and government agency obligations	51,402		—		(193		)	51,209
Municipal bonds	17,930		5		(11		)	17,924
Equity securities	17,005		14,462		—			31,467
	$	856,429	$	14,623	$	(2,769	)	$	868,283

The Company classifies its debt security investments based on their contractual maturity dates. The debt securities listed as of September 30, 2016 mature at various dates through September 2021. The fair values of debt security investments by contractual maturity consist of the following:



	September 30, 2016		December 31, 2015
Maturities within one year	$	443,875	$	236,121
Maturities after one year through five years	759,842		600,695
	$	1,203,717	$	836,816

The following table shows the fair value of the Company's marketable 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, 2016	Fair Value		Unrealized Loss			Fair Value		Unrealized Loss			Fair Value		Unrealized Loss
Unrestricted
Corporate bonds	$	354,112	$	(475	)	$	52,787	$	(86	)	$	406,899	$	(561	)
U.S. government and government agency obligations	29,200		(40		)	—		—			29,200		(40		)
Municipal bonds	1,529		(1		)	—		—			1,529		(1		)
Equity securities	7,435		(7,565		)	—		—			7,435		(7,565		)
	392,276		(8,081		)	52,787		(86		)	445,063		(8,167		)
Restricted
Equity securities	44,157		(5,843		)	—		—			44,157		(5,843		)
	$	436,433	$	(13,924	)	$	52,787	$	(86	)	$	489,220	$	(14,010	)

As of December 31, 2015
Corporate bonds	$	668,199	$	(2,473	)	$	23,749	$	(92	)	$	691,948	$	(2,565	)
U.S. government and government agency obligations	51,215		(193		)	—		—			51,215		(193		)
Municipal bonds	11,917		(11		)	—		—			11,917		(11		)
	$	731,331	$	(2,677	)	$	23,749	$	(92	)	$	755,080	$	(2,769	)

Realized gains and losses on sales of marketable securities were not material for the three and nine months ended September 30, 2016 and 2015.

Changes in the Company's accumulated other comprehensive income (loss) for the three and nine months ended September 30, 2016 and 2015 related to unrealized gains and losses on available-for-sale marketable securities. For the three and nine months ended September 30, 2016 and 2015, amounts reclassified from accumulated other comprehensive income (loss) into investment income in the Company's Statements of Operations were related to realized gains and losses on sales of marketable securities.

- Definition

The entire disclosure for investments in certain debt and equity securities.

+ References + Details

Fair Value Measurements (Notes)

9 Months Ended

Sep. 30, 2016

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, 2016	Fair Value		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Available-for-sale marketable securities:
Unrestricted
Corporate bonds	$	967,921	—		$	967,921
U.S. government and government agency obligations	116,096		—		116,096
Municipal bonds	10,225		—		10,225
Commercial paper	73,419		—		73,419
Certificates of deposit	36,056		—		36,056
Equity securities	18,064		$	18,064	—
	1,221,781		18,064		1,203,717
Restricted
Equity securities	44,157		—		44,157
	$	1,265,938	$	18,064	$	1,247,874

As of December 31, 2015
Available-for-sale marketable securities:
Unrestricted
Corporate bonds	$	767,683	—		$	767,683
U.S. government and government agency obligations	51,209		—		51,209
Municipal bonds	17,924		—		17,924
Equity securities	31,467		$	31,467	—
	$	868,283	$	31,467	$	836,816

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, 2016 and 2015.

There were no purchases, sales, or maturities of Level 3 marketable securities and no unrealized gains or losses related to Level 3 marketable securities for the three and nine months ended September 30, 2016 and 2015. During the nine months ended September 30, 2015, transfers of marketable securities from Level 2 to Level 1 were $91.4 million in connection with the lapse of the transfer restrictions on the Company's investment in Adverum Biotechnologies, Inc. (formerly Avalanche Biotechnologies, Inc.) common shares in January 2015. The Company's policy for recognition of transfers between levels of the fair value hierarchy is to recognize any transfer at the beginning of the fiscal quarter in which the determination to transfer was made. There were no other transfers of marketable securities between Levels 1, 2, or 3 classifications during the nine months ended September 30, 2016 and 2015. The Company's investment in Intellia common stock was classified as a Level 2 marketable security as of September 30, 2016 (see Note 5).

As of September 30, 2016 and December 31, 2015, the Company had $0.2 million and $11.2 million, respectively, in aggregate principal amount of 1.875% convertible senior notes (the "Notes") outstanding that matured in October 2016 (see Note 9). The fair value of the outstanding Notes was estimated to be $72.8 million as of December 31, 2015, and was determined based on Level 2 inputs, such as market and observable sources. The fair value of the outstanding Notes as of September 30, 2016 was not material.

- 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

Inventory (Notes)

9 Months Ended

Sep. 30, 2016

Inventory Disclosure [Abstract]

Inventory

Inventories

Inventories consist of the following:



	September 30,		December 31,
	2016		2015
Raw materials	$	89,675	$	59,151
Work-in-process	164,062		132,068
Finished goods	16,980		11,197
Deferred costs	74,903		36,162
	$	345,620	$	238,578

Deferred costs represent the costs of product manufactured and shipped to the Company's collaborators for which recognition of revenue has been deferred. For the three months ended September 30, 2016 and 2015, cost of goods sold included inventory write-downs and reserves totaling $5.0 million and $1.8 million, respectively. For the nine months ended September 30, 2016 and 2015, cost of goods sold included inventory write-downs and reserves totaling $11.3 million and $9.9 million, respectively.

Debt (Notes)	9 Months Ended
Debt (Notes)	Sep. 30, 2016
Debt Disclosure [Abstract]
Debt Disclosure [Text Block]	Debt a. Convertible Debt In the first nine months of 2016, the Company settled conversion obligations for $12.7 million principal amount of the Company's Notes that was previously surrendered for conversion. Consequently, in the first nine months of 2016, the Company paid $12.7 million in cash and issued 118,822 shares of Common Stock. In addition, the Company allocated $47.1 million of the settlement consideration provided to the Note holders to the reacquisition of the equity component of the Notes, and recognized such amount as a reduction of stockholder's equity. The loss on the debt extinguishment in connection with the Notes that were surrendered for conversion during the first nine months of 2016 was not material. As a result of these Note conversions, in the first nine months of 2016, the Company also exercised a proportionate amount of its convertible note hedges, for which the Company received 118,808 shares of Common Stock, which was approximately equal to the number of shares the Company was required to issue to settle the non-cash portion of the related Note conversions. The Company recorded the cost of the shares received, or $10.0 million, as Treasury Stock during the first nine months of 2016. The aggregate principal amount of Notes that remained outstanding as of September 30, 2016 was $0.2 million, which subsequently matured in October 2016. In the first nine months of 2015, the Company settled conversion obligations for $146.0 million principal amount of the Company's Notes. Upon settlement of the Notes, the Company paid $146.0 million in cash and issued 1,419,287 shares of Common Stock. In addition, in the first nine months of 2015, the Company allocated $705.9 million of the settlement consideration provided to the Note holders to the reacquisition of the equity component of the Notes, and recognized such amount as a reduction of stockholder's equity. In addition, the Company recognized a $16.9 million loss during the first nine months of 2015 on the debt extinguishment. In connection with the Note conversions in the first nine months of 2015, the Company also exercised a proportionate amount of its convertible note hedges, for which the Company received 1,419,268 shares of Common Stock, which was approximately equal to the number of shares the Company was required to issue to settle the non-cash portion of the related Note conversions. The Company recorded the cost of the shares received, or $119.2 million, as Treasury Stock during the first nine months of 2015. Warrant Transactions In November 2015, the Company entered into an amendment agreement with a warrant holder whereby the parties agreed to reduce a portion of the number of warrants held by the warrant holder. The reduction in the number of warrants was determined based on the number of warrants with respect to which the warrant holder closed out its hedge position, provided that the warrant holder did not effect any purchases at a price per share exceeding $535.00 per share, during the period starting on November 16, 2015 and ending no later than February 9, 2016. The Company was able to settle, at its option, any payments due under the amendment agreement in cash or by delivering shares of Common Stock. As a result of the warrant holder closing out a portion of its hedge position in the first quarter of 2016, the Company paid a total of $135.2 million to reduce the number of warrants held by such warrant holder by 360,406 (which was the remaining maximum number of warrants to be reduced subject to the amendment agreement). In February 2016, the Company entered into an amendment agreement with a warrant holder whereby the parties agreed to reduce a portion of the number of warrants held by the warrant holder by up to a maximum of 975,142. The reduction in the number of warrants was determined based on the number of warrants with respect to which the warrant holder closed out its hedge position, provided that the warrant holder did not effect any purchases at a price per share exceeding $375.00 per share, during the period starting on February 22, 2016 and ending no later than May 5, 2016. The Company was able to settle, at its option, any payments due under the amendment agreement in cash or by delivering shares of Common Stock. As a result of the warrant holder closing out a portion of its hedge position during the first half of 2016, the Company paid a total of $106.9 million to reduce the number of warrants held by such warrant holder by 403,665. As of September 30, 2016, an aggregate of 1,345,027 warrants (subject to adjustment from time to time as provided in the applicable warrant agreements) remained outstanding. In November 2014, the Company entered into an amendment agreement with a warrant holder whereby the parties agreed to reduce a portion of the number of warrants held by the warrant holder. The reduction in the number of warrants was determined based on the number of warrants with respect to which the warrant holder had closed out its hedge position, provided that the warrant holder did not effect any purchases at a price per share exceeding $397.75 per share, during the period starting on November 26, 2014 and ending no later than February 12, 2015. The Company was obligated to settle any payments due under the amendment agreement in February 2015. Given that the amendment agreement contained a conditional obligation that required settlement in cash, and the Company's obligation was indexed to the Company's share price, the Company reclassified the estimated fair value of the warrants subject to the agreement from additional paid-in capital to a liability in November 2014, with such liability subsequently measured at fair value with changes in fair value recognized in earnings. In February 2015, the Company paid a total of $124.0 million to reduce the number of warrants held by such warrant holder by 416,480. Upon expiration of the November 2014 amended agreement, in the first quarter of 2015 the remaining warrants were re-measured at fair value, and $23.3 million was reclassified back to additional paid-in capital, consistent with the original classification of the warrants under the 2011 issuance. Total losses related to changes in fair value of the warrants during the first quarter of 2015 were not material. In addition to the November 2014 warrant transaction described above, during the first nine months of 2015, the Company entered into agreements to reduce the number of warrants held by warrant holders. Pursuant to the agreements, the Company paid an aggregate amount of $399.5 million to the warrant holders during 2015 to reduce the number of shares of Common Stock issuable upon exercise of the warrant by 898,547 in the aggregate. b. Credit Facility In March 2015, the Company entered into an agreement with a syndicate of lenders which provides for a $750.0 million senior unsecured five-year revolving credit facility. As of September 30, 2016, the Company had no borrowings outstanding under the credit facility and was in compliance with all credit facility covenants.

Income Taxes (Notes)	9 Months Ended
Income Taxes (Notes)	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company is subject to U.S. federal, state, and foreign income taxes. The Company recorded an income tax provision in its Statement of Operations of $101.1 million and $182.9 million for the three months ended September 30, 2016 and 2015, respectively, and $345.9 million and $516.7 million for the nine months ended September 30, 2016 and 2015, respectively. The Company's effective tax rate was 27.6% and 46.5% for the three months ended September 30, 2016 and 2015, respectively, and 35.0% and 51.8% for the nine months ended September 30, 2016 and 2015, respectively. The Company's effective tax rate for the three and nine months ended September 30, 2016 was positively impacted, compared to the U.S. federal statutory rate, by the tax benefit associated with stock-based compensation (see Note 13), the domestic manufacturing deduction, and the federal tax credit for increased research activities, offset by the negative impact of losses incurred in foreign jurisdictions with rates lower than the U.S. federal statutory rate and the non-tax deductible Branded Prescription Drug Fee. The Company's effective tax rate for the three months ended September 30, 2016 was also positively impacted by changes to tax reserves. The Company's effective tax rate for the three and nine months ended September 30, 2015 was negatively impacted, compared to the U.S. federal statutory rate, by losses incurred in foreign jurisdictions with rates lower than the U.S. federal statutory rate, the non-deductible Branded Prescription Drug Fee, and expiration, at the end of 2014, of the federal tax credit for increased research activities. The negative impact of these items was partly offset by the positive impact of the domestic manufacturing deduction. The Company also recorded an income tax benefit in its Statement of Comprehensive Income of $1.7 million and $6.5 million for the three months ended September 30, 2016 and 2015, respectively, and $3.3 million and $25.4 million for the nine months ended September 30, 2016 and 2015, respectively, primarily related to unrealized losses on available-for-sale marketable securities.

Statement of Cash Flows (Notes)	9 Months Ended
Statement of Cash Flows (Notes)	Sep. 30, 2016
Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract]
Statement of Cash Flows	Statement of Cash Flows Supplemental disclosure of non-cash investing and financing activities Included in accounts payable and accrued expenses as of September 30, 2016 and December 31, 2015 were $33.9 million and $50.7 million, respectively, of accrued capital expenditures. Included in accounts payable and accrued expenses as of September 30, 2015 and December 31, 2014 were $84.7 million and $56.2 million, respectively, of accrued capital expenditures. Included in accounts payable and accrued expenses as of December 31, 2014 was $7.5 million for the Company's conversion settlement obligation related to the Company's Notes which were surrendered for conversion but not settled as of December 31, 2014. The amount of such liability was not material as of September 30, 2016, September 30, 2015, and December 31, 2015. Included in accounts payable and accrued expenses as of December 31, 2014 was $59.8 million related to the Company's payment obligation for a reduction in the number of warrants based on a warrant holder closing out a portion of its hedge position. Additionally, included within other current liabilities as of December 31, 2014 was $87.5 million in connection with the estimated fair value of the remaining warrant liability. There were no such liabilities recorded in connection with warrants as of September 30, 2016, December 31, 2015, and September 30, 2015. The Company recognized an additional facility lease obligation of $16.4 million and $27.0 million during the nine months ended September 30, 2016 and 2015, respectively, in connection with capitalizing, on the Company's books, the landlord's costs of constructing new facilities that the Company has leased.

Legal Matters (Notes)	9 Months Ended
Legal Matters (Notes)	Sep. 30, 2016
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. 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 altered 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). At this time, the Company is not able to predict the outcome of, or estimate possible gain or a range of possible loss, if any, related to, these proceedings. Proceedings Relating to Praluent (alirocumab) Injection On October 17, 2014 and October 28, 2014, Amgen Inc. filed complaints against Regeneron, Sanofi, Aventisub LLC (subsequently removed and replaced with Sanofi-Aventis U.S. LLC), and Aventis Pharmaceuticals, Inc. in the United States District Court for the District of Delaware seeking an injunction to prohibit Regeneron and the other defendants from manufacturing, using, offering to sell, or selling within the United States (as well as importing into the United States) Praluent, which Regeneron is jointly developing with Sanofi. On November 11, 2014 and November 17, 2014 Amgen filed complaints against Regeneron, Sanofi, Sanofi-Aventis U.S. LLC, and Aventis Pharmaceuticals, Inc. in the same court seeking the same relief. Amgen asserts U.S. Patent Nos. 8,563,698, 8,829,165 (the "'165 Patent"), and 8,859,741 (the "'741 Patent") in the first complaint, U.S. Patent Nos. 8,871,913 and 8,871,914 (the "'914 Patent") in the second complaint, U.S. Patent No. 8,883,983 in the third complaint, and U.S. Patent No. 8,889,834 in the fourth complaint. 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. On December 15, 2014, all of the four proceedings were consolidated into a single case. On September 15, 2015, Amgen filed a motion for leave to file a supplemental and second amended complaint, which was granted on January 29, 2016. As amended, the complaint alleges, among other things, willful infringement of the asserted patents, which would allow the court to increase damages up to three times the amount assessed if the court finds willful infringement. On October 20, 2015, the District Court issued its claim construction order, in which it defined the meaning of certain disputed claim terms; none of the court's rulings were dispositive of the issues in the case. On November 3, 2015, pursuant to court order, the patents asserted by Amgen were narrowed to the '165, '741, and '914 Patents. On March 4, 2016, Amgen further narrowed the asserted patents to the '165 and '741 Patents. A jury trial in this litigation was held from March 8 to March 16, 2016. During the course of the trial, the court ruled as a matter of law in favor of Amgen that the asserted patent claims were not obvious, and in favor of Regeneron and Sanofi that there was no willful infringement of the asserted patent claims by Regeneron or Sanofi. 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 March 23 and March 24, 2016, the court held a permanent injunction hearing to determine whether Regeneron and Sanofi should be prohibited from commercializing Praluent. The parties to this litigation submitted post-trial briefs in the second quarter of 2016 and are awaiting the court's final opinion and judgment, including a decision on the permanent injunction. The Company and Sanofi plan to appeal any judgment or order that is adverse to the Company and Sanofi. 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 an injunction, damages, an accounting of profits, and costs and interest. 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, seeking an injunction, an accounting of marketing activities, a recall of Praluent and its removal from distribution channels, and damages. 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., and Sanofi Winthrop Industrie. 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. At this time, the Company is not able to predict the outcome of, or estimate a range of possible loss, if any, related to these proceedings. Proceedings Relating to Patents Owned by Genentech and City of Hope On July 27, 2015, the Company and Sanofi-Aventis U.S. LLC filed a complaint in the United States District Court for the Central District of California (Western Division) seeking a declaratory judgment of invalidity, as well as non-infringement by the manufacture, use, sale, offer of sale, or importation of Praluent (alirocumab), of U.S. Patent No. 7,923,221 (the "'221 Patent") jointly owned by Genentech, Inc. ("Genentech") and City of Hope relating to the production of recombinant antibodies by host cells. On the same day, the Company and Sanofi-Aventis U.S. LLC ("Sanofi-Aventis") initiated an inter partes review in the United States Patent and Trademark Office ("USPTO") seeking a declaration of invalidity of certain claims of U.S. Patent No. 6,331,415 (the "'415 Patent" and, together, with the "221 Patent", the "Cabilly Patents") jointly owned by Genentech and City of Hope relating to the production of recombinant antibodies by host cells. On February 5, 2016, the USPTO instituted an inter partes review of the validity of most of the patent claims of the '415 Patent for which review had been requested. On September 17, 2015, Genentech and City of Hope answered the complaint previously filed by the Company and Sanofi concerning the '221 Patent in the District Court and counterclaimed, alleging that the Company and Sanofi infringe the '221 Patent and seeking, among other types of relief, damages and a permanent injunction. On August 18, 2016, Regeneron and Sanofi-Aventis entered into a License and Settlement Agreement with Genentech and City of Hope that resolved all outstanding issues concerning the Cabilly Patents in the above-referenced litigation and inter partes review proceeding, resulting in a joint stipulation of dismissal being entered in the court and the USPTO. Under the agreement, Regeneron has been granted a license to the Cabilly Patents to make, use, and sell Praluent and all other antibody products under development at the time of the settlement. 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 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 2014 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 March 2, 2016, the defendants filed a motion to dismiss the shareholder derivative complaint. On August 16, 2016, the court heard oral argument on defendants' motion to dismiss. 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. The demand asserts that the 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 demand requests 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. The Company's board of directors, working with outside counsel, investigated the allegations in the demand and the shareholder derivative complaint, and has determined to defer its decision on the demand until the court rules on the pending motion to dismiss the shareholder derivative complaint, as discussed above. At this time, the Company is not able to predict the outcome of, or estimate a range of possible loss, if any, relating to these matters.

Recently Issued Accounting Standards (Notes)	9 Months Ended
Recently Issued Accounting Standards (Notes)	Sep. 30, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	Recently Issued Accounting Standards In March 2016, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update 2016-09 ("ASU 2016-09"), Compensation - Stock Compensation, Improvements to Employee Share-Based Payment Accounting, which the Company elected to early adopt during the second quarter of 2016. ASU 2016-09 requires an entity to recognize all excess tax benefits and tax deficiencies in connection with stock-based compensation as income tax expense or benefit in the income statement (previously, excess tax benefits were recognized in additional paid-in capital). This aspect of ASU 2016-09 was adopted prospectively, and accordingly, the Company recorded excess tax benefits of $8.6 million and $64.1 million, respectively, within income tax expense for the three and nine months ended September 30, 2016, respectively. Included within income tax expense for the nine months ended September 30, 2016 is $15.6 million of excess tax benefits, which was previously recorded to additional paid-in capital during the first quarter of 2016. The amendments also require recognition of excess tax benefits regardless of whether the benefit reduces taxes payable in the current period. Furthermore, the amendments require that excess tax benefits be classified as an operating activity in the statement of cash flows (such amounts were previously included as a financing activity in the statement of cash flows); the Company also adopted this provision of ASU 2016-09 prospectively. In February 2016, the FASB issued Accounting Standards Update 2016-02, Leases. The new standard requires a lessee to recognize in its balance sheet (for both finance and operating leases) a liability to make lease payments ("lease liability") 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. The Company is evaluating the impact that this guidance will have on the Company's financial statements. In January 2016, the FASB issued Accounting Standards Update 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. The amendments require equity investments (except those accounted for under the equity method of accounting or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income. The amendments are effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. The implementation of the amendments is expected to increase the volatility of an entity's net income; however, the Company is not currently able to estimate the impact of adopting these amendments, as the significance of the impact will depend on the Company's equity investment balance upon adoption. In May 2014, the FASB issued Accounting Standards Update 2014-09, Revenue from Contracts with Customers, which will replace existing revenue recognition guidance. The new standard requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. To achieve that core principle, an entity must identify the contract(s) with a customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies the performance obligation. In July 2015, the FASB decided to delay the effective date of the new standard by one year; as a result, the new standard will be effective for annual and interim reporting periods beginning after December 15, 2017. Early adoption will be permitted, but no earlier than 2017 for calendar year-end entities. The standard allows for two transition methods - retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of initially applying the standard recognized at the date of initial adoption. The Company has not yet determined its method of transition and is evaluating the impact that this guidance will have on the Company's financial statements.

Net Product Sales (Policies)	9 Months Ended
Net Product Sales (Policies)	Sep. 30, 2016
Revenues [Abstract]
Revenue Recognition, Revenue Reductions [Policy Text Block]	Revenue from product sales is recorded net of applicable provisions for rebates and chargebacks, distribution-related fees, and other sales-related deductions.

Fair Value Measurements (Policies)	9 Months Ended
Fair Value Measurements (Policies)	Sep. 30, 2016
Fair Value Disclosures [Abstract]
Fair Value Transfer, Policy [Policy Text Block]	The Company's policy for recognition of transfers between levels of the fair value hierarchy is to recognize any transfer at the beginning of the fiscal quarter in which the determination to transfer was made.