Revenue from Contract with Customer [Abstract] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Project [Axis] Project [Axis] Project [Domain] Project [Domain] Sanofi Collaboration Agreement, Immuno-oncology Sanofi Collaboration Agreement, Immuno-oncology [Member] Sanofi Collaboration Agreement, Immuno-oncology [Member] Research and Development Arrangement Contract to Perform for Others by Product [Axis] Research and Development Arrangement Contract to Perform for Others by Product [Axis] Research and Development Arrangement Contract to Perform for Others by Product [Axis] Research and Development Arrangement Contract to Perform for Others by Product [Domain] Research and Development Arrangement Contract to Perform for Others by Product [Domain] [Domain] for Research and Development Arrangement Contract to Perform for Others by Product [Axis] IO Discovery Agreement [Member] IO Discovery Agreement [Member] In July 2015, the Company entered into a collaboration agreement (Immuno-Oncology agreement) with Sanofi, to jointly develop and commercialize Immuno-Oncology programs. IO Agreement [Member] IO Agreement [Member] IO Agreement IO License and Collaboration Agreement [Member] IO License and Collaboration Agreement [Member] In July 2015, the Company entered into a Immuno-oncology License and Collaboration Agreement (the "IO License and Collaboration Agreement") with Sanofi, to jointly develop and commercialize Immuno-oncology products. Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] PD-1 [Member] PD-1 [Member] Programed Cell Death protein 1, or PD-1 ("REGN2810") Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Up-front payment received Up-front payment received Up-front payment received upon the execution of a collaboration agreement. License agreement term License agreement term Potential agreement term, from the effective date of agreement. Additional years to extend the agreement Additional years to extend the agreement Additional years to extend the agreement Maximum amount of shared development costs Maximum amount of shared development costs The maximum amount of shared development expenses for PD-1. Increase amount of shared development costs Increase amount of shared development costs Increase amount of shared development costs Maximum shares the collaborator could sell (in shares) Maximum shares the collaborator could sell Maximum shares the collaborator could sell through September 30, 2020. Treasury stock, shares acquired Treasury Stock, Shares, Acquired Cost of Treasury stock shares received Treasury Stock, Value, Acquired, Cost Method Maximum amount of sales milestone payments if total sales achieve specific levels Maximum amount of sales milestone payments if total sales achieve specific levels The maximum amount of sales milestone payments the Company is eligible to receive when and if total annual sales achieve certain specified levels. Levels of twelve month sales at which sales milestone payments would be received Levels of twelve month sales at which sales milestone payments would be received Aggregate amount of twelve month sales upon which sales milestone would be received. Period for achieving sales target for milestone payment, rolling basis Period for Achieving Sales Target for Milestone Payment, Rolling Basis Period for Achieving Sales Target for Milestone Payment, Rolling Basis Remaining performance obligation Revenue, Remaining Performance Obligation, Amount Derivative Instruments and Hedging Activities Disclosure [Abstract] Derivative [Table] Derivative [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest rate swap contracts Interest Rate Swap [Member] Interest rate cap contracts Interest Rate Cap [Member] Derivative [Line Items] Derivative [Line Items] Derivative, Notional Amount Derivative, Notional Amount Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness Gain (Loss) on Interest Rate Cash Flow Hedge Ineffectiveness Accounting Policies [Abstract] Recently Issued Accounting Standards Description of New Accounting Pronouncements Not yet Adopted [Text Block] Supplemental Cash Flow Information [Abstract] Statement of Cash Flows Cash Flow, Supplemental Disclosures [Text Block] Revenues [Abstract] Revenue Recognition, Multiple-deliverable Arrangements [Table] Revenue Recognition, Multiple-deliverable Arrangements [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] UNITED STATES UNITED STATES EYLEA EYLEA Net Product Sales [Member] Revenue during the period derived from a specified product line (EYLEA), after deducting applicable provisions for discounts, returns, rebates, chargebacks, distribution fees, and other sales-related deductions. ARCALYST Arcalyst Net Product Sales [Member] Revenue during the period derived from a specified product line (ARCALYST), after deducting applicable provisions for discounts, returns, rebates, chargebacks, distribution fees, and other sales-related deductions. Product Product [Member] Revenue Recognition, Multiple-deliverable Arrangements [Line Items] Revenue Recognition, Multiple-deliverable Arrangements [Line Items] Revenues Revenue from Contract with Customer, Excluding Assessed Tax Document And Entity Information [Abstract] -- None. No documentation exists for this element. -- Entities [Table] Class of Stock [Axis] Class of Stock [Domain] Common Stock Common Stock [Member] Class A Stock Common Class A [Member] Entity Information [Line Items] Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Earnings Per Share [Abstract] Basic and Diluted Net Income (Loss) Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Antidilutive Securities Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Investments, Debt and Equity Securities [Abstract] Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Bayer Bayer HealthCare LLC. Collaboration Agreement [Member] Bayer HealthCare LLC. Collaboration Agreement Increase (decrease) in deferred revenue Increase (Decrease) in Contract with Customer, Liability Revenue recognized that was included in deferred revenue at the beginning of the period Contract with Customer, Liability, Revenue Recognized Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Stock options Employee Stock Option [Member] Restricted stock Restricted Stock [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Weighted average number of shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Condensed Cash Flow Statement [Table] Condensed Cash Flow Statement [Table] Condensed Cash Flow Statements, Captions [Line Items] Condensed Cash Flow Statements, Captions [Line Items] Accrued capital expenditures Accrued Capital Expenditures Carrying value as of the balance sheet date of obligations incurred and payable for purchases of fixed assets. Included in accounts payable and accrued expenses. Capital lease obligations incurred Capital Lease Obligations Incurred Collaboration Agreements Collaborative Arrangement Disclosure [Text Block] Inventory Disclosure [Abstract] Inventories Inventory Disclosure [Text Block] Fair Value Disclosures [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] Product and service, other Product and Service, Other [Member] Reimbursement of Regeneron research and development expenses Reimbursement Of Research And Development Expenses [Member] Reimbursement Of Research And Development Expenses [Member] Reimbursement of Regeneron commercialization-related expenses Reimbursement Of Commercialization-Related Expenses [Member] Reimbursement Of Commercialization-Related Expenses [Member] Regeneron's share of losses in connection with commercialization of antibodies Share Of Losses In Connection With Commercialization [Member] Share Of Losses In Connection With Commercialization [Member] Other Other [Member] Other [Member] Sanofi Collaboration Agreement, Antibody Sanofi Collaboration Agreement, Antibody [Member] Sanofi Collaboration Agreement, Antibody [Member] Sanofi Sanofi Collaboration Agreement [Member] Sanofi Collaboration Agreement [Member] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Corporate bonds Corporate Bond Securities [Member] U.S. government and government agency obligations US Treasury and Government [Member] Municipal bonds Municipal Bonds [Member] Commercial paper Commercial Paper [Member] Certificates of deposit Certificates of Deposit [Member] Classification of Investment [Axis] Classification of Investment [Axis] This element represents the general categories of investments, which may be classified as Unrestricted or Restricted. Classification of Investment [Domain] Classification of Investment [Domain] Provides general categories of investments for which information is required or determined to be disclosed. Unrestricted Unrestricted [Member] Investments whose use is not restricted in whole or in part, by contractual agreements or regulatory requirements. Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Amortized Cost Basis Debt Securities, Available-for-sale, Amortized Cost Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Fair Value Debt Securities, Available-for-sale Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Gross Sales Revenue Gross Sales Revenue [Member] Gross Sales Revenue [Member] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Customer concentration risk Customer Concentration Risk [Member] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] Besse Medical, a subsidiary of AmerisourceBergen Corporation Besse Medical [Member] Besse Medical [Member] McKesson Corporation McKesson Corporation [Member] McKesson Corporation [Member] Curascript SD Specialty Distribution, a subsidiary of Express Scripts Curascript SD [Member] Curascript SD [Member] Concentration risk, percentage Concentration Risk, Percentage Schedule of Notional Amounts of Outstanding Derivative Positions Schedule of Notional Amounts of Outstanding Derivative Positions [Table Text Block] Schedule of Inventory, Current Schedule of Inventory, Current [Table Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] Other Other Collaboration Agreements [Member] Other Collaboration Agreements [Member] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2014-09 Accounting Standards Update 2014-09 [Member] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Axis] Initial Application Period Cumulative Effect Transition [Domain] Initial Application Period Cumulative Effect Transition [Domain] Adjustments Difference between Revenue Guidance in Effect before and after Topic 606 [Member] Balance Without Adoption of ASC 606 Calculated under Revenue Guidance in Effect before Topic 606 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Income from operations Operating Income (Loss) Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Net income Net Income (Loss) Attributable to Parent Product Sales Product Sales and Concentration Risk [Text Block] Product Sales and Concentration Risk Disclosure [Text Block] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Other than temporary impairment losses, investments Other than Temporary Impairment Losses, Investments Fair value, assets, level 1 to level 2 transfers, amount Fair Value, Assets, Level 1 to Level 2 Transfers, Amount Securities owned not readily marketable Securities Owned Not Readily Marketable Schedule of assets measured at fair value on a recurring basis Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block] Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities Disclosure [Text Block] Deferred tax assets Deferred Income Tax Assets, Net Total assets Assets Accrued expenses and other current liabilities Accrued Liabilities and Other Liabilities Deferred revenue, current Contract with Customer, Liability, Current Total current liabilities Liabilities, Current Deferred revenue, noncurrent Contract with Customer, Liability, Noncurrent Total liabilities Liabilities Retained earnings Retained Earnings (Accumulated Deficit) Total stockholders' equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders' equity Liabilities and Equity Accounts receivable, net Accounts Receivable, Related Parties, Current Deferred revenue Contract with Customer, Liability Schedule of collaboration revenue Disaggregation of Revenue [Table Text Block] Schedule of accounts receivable and deferred revenue information Contract with Customer, Asset and Liability [Table Text Block] Statement of Cash Flows [Abstract] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization Non-cash compensation expense Share-based Compensation Other non-cash items, net Other Noncash Income (Expense) Deferred taxes Increase (Decrease) in Deferred Income Taxes Changes in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Increase in Sanofi, Bayer, and trade accounts receivable Increase (Decrease) in Accounts Receivable Increase in inventories Increase (Decrease) in Inventories Decrease (increase) in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Increase (decrease) in accounts payable, accrued expenses, and other liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Total adjustments Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Purchases of marketable and other securities Payments to Acquire Marketable Securities Sales or maturities of marketable securities Proceeds from Sale and Maturity of Marketable Securities Capital expenditures Payments to Acquire Productive Assets Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Proceeds in connection with capital and facility lease obligations Proceeds from (Repayments of) Long-term Debt and Capital Securities Payments in connection with capital and facility lease obligations Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities Proceeds from issuance of Common Stock Proceeds from Issuance of Common Stock Payments in connection with Common Stock tendered for employee tax obligations Payments Related to Tax Withholding for Share-based Compensation Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Net increase in cash, cash equivalents, and restricted cash Cash and Cash Equivalents, Period Increase (Decrease) Cash, cash equivalents, and restricted cash at beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash, cash equivalents, and restricted cash at end of period Schedule of product sales Schedules of Concentration of Risk, by Risk Factor Schedules of Concentration of Risk, by Risk Factor [Table Text Block] Sales Related Deductions Activity Schedule of Sales Related Deductions Activity [Table Text Block] Tabular disclosure of the activity of sales-related deductions during the period, which includes rebates, chargebacks, discounts, and distributor-related fees. Teva Pharmaceuticals Collaboration Agreement [Member] Teva Pharmaceuticals Collaboration Agreement [Member] Teva Pharmaceuticals Collaboration Agreement [Member] Increase as a result of cumulative-effect adjustment arising from the adoption of ASC 606 Available-for-sale Debt Securities Debt Securities, Available-for-sale [Table Text Block] Marketable Securities, Based on Contractual Maturity Dates Investments Classified by Contractual Maturity Date [Table Text Block] Fair Value and Unrealized Losses of Marketable Securities Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block] Net income - basic and diluted Weighted average shares outstanding - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of dilutive securities: Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Stock options (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Restricted stock (in shares) Incremental Common Shares Attributable To Nonvested Restricted Shares Nonvested equity-based payment awards that result in incremental common shares. Dilutive potential shares (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Weighted average shares - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Net income per share - basic (in dollars per share) Earnings Per Share, Basic Net income per share - diluted (in dollars per share) Earnings Per Share, Diluted Statement of Comprehensive Income [Abstract] Statement [Table] Statement [Table] Collaboration and contract manufacturing Collaboration and Contract Manufacturing [Member] Collaboration and Contract Manufacturing [Member] Statement [Line Items] Statement [Line Items] Statements of Operations Income Statement [Abstract] Revenues: Expenses: Costs and Expenses [Abstract] Research and development Research and Development Expense Selling, general, and administrative Selling, General and Administrative Expense Cost of goods sold Cost of Goods and Services Sold Total expenses Costs and Expenses Income from operations Other income (expense): Nonoperating Income (Expense) [Abstract] Other income (expense), net Other Nonoperating Income (Expense) Interest expense Interest Expense Total other income (expense) Nonoperating Income (Expense) Income before income taxes Net income Weighted average shares - diluted (in shares) Statements of Comprehensive Income Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unrealized gain (loss) on marketable securities Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Unrealized gain on cash flow hedges Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Current assets: Assets, Current [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Marketable securities Marketable Securities, Current Accounts receivable - trade, net Accounts Receivable, Net, Current Accounts receivable from Sanofi Accounts receivable from Bayer Accounts and Notes Receivable, Net Inventories Inventory, Net Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Total current assets Assets, Current Marketable securities Marketable Securities, Noncurrent Property, plant, and equipment, net Property, Plant and Equipment, Net Other noncurrent assets Other Assets, Noncurrent Total assets LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable Total current liabilities Capital and facility lease obligations Capital and facility lease obligations, noncurrent Represents the noncurrent portion of a lease liability Other noncurrent liabilities Other Liabilities, Noncurrent Total liabilities Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Preferred Stock, $.01 par value; 30,000,000 shares authorized; issued and outstanding - none Preferred Stock, Value, Issued Common stock Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Accumulated other comprehensive (loss) income Accumulated Other Comprehensive Income (Loss), Net of Tax Treasury Stock, at cost; 3,885,469 shares in 2018 and 3,763,868 shares in 2017 Treasury Stock, Value Total stockholders' equity Total liabilities and stockholders' equity Commitments and Contingencies Disclosure [Abstract] Legal Matters Legal Matters and Contingencies [Text Block] Equity Securities Equity Securities [Member] Accounting Standards Update 2016-01 Accounting Standards Update 2016-01 [Member] Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Axis] Adjustments for Change in Accounting Principle [Domain] Adjustments for Change in Accounting Principle [Domain] Cumulative effect on retained earnings, net of tax Cumulative Effect on Retained Earnings, Net of Tax Reclassification from accumulated other comprehensive income, current period, before tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Table] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves Type [Axis] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] SEC Schedule, 12-09, Valuation Allowances and Reserves [Domain] Rebates, Chargebacks, and Discounts Rebates and Chargebacks [Member] A valuation allowance for rebates and chargebacks under governmental programs (including Medicaid), which are netted against revenue from product sales. Distribution- Related Fees Distribution Related Fees [Member] A valuation allowance for distribution-related fees which are netted against revenue from product sales. Other Sales- Related Deductions Other Sales Related Deductions [Member] A valuation allowance for other sales-related deductions which are netted against revenue from product sales. SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items] Beginning Balance SEC Schedule, 12-09, Valuation Allowances and Reserves, Amount Provisions SEC Schedule, 12-09, Valuation Allowances and Reserves, Additions, Charge to Other Account Credits/payments SEC Schedule, 12-09, Valuation Allowances and Reserves, Deduction Ending Balance Accounts receivable, net Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Research and Development Arrangement, Contract to Perform for Others, Type [Axis] Research and Development Arrangement, Contract to Perform for Others, Type [Axis] Research and Development Arrangement, Contract to Perform for Others, Type [Domain] Research and Development Arrangement, Contract to Perform for Others, Type [Domain] Ang2 Antibody Ang2 Antibody [Member] Ang2 Antibody [Member] Revenue based on percentage of annual sales in Japan Revenue based on percentage of annual sales in Japan The percentage on annual sales in Japan that the Company is entitled to receive, subject to certain potential adjustments. Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Estimate of Fair Value Measurement Estimate of Fair Value Measurement [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Measured on a recurring basis Fair Value, Measurements, Recurring [Member] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Available-for-sale debt securities: Debt Securities, Available-for-sale [Abstract] Corporate bonds Financial Instruments, Owned, Corporate Debt, at Fair Value U.S. government and government agency obligations Financial Instruments, Owned, US Government and Agency Obligations, at Fair Value Municipal bonds Municipal Debt Securities, at Carrying Value Commercial paper Commercial Paper, at Carrying Value Certificates of deposit Certificates of Deposit, at Carrying Value Equity securities Equity Securities, FV-NI Total marketable securities Marketable Securities Net Income Per Share Earnings Per Share [Text Block] Restricted cash included in Other noncurrent assets Restricted Cash Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statement of Cash Flows Fair Value - Less than 12 Months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Unrealized Loss - Less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Fair Value - 12 Months or Greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Unrealized Loss - 12 Months or Greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Fair Value - Total Debt Securities, Available-for-sale, Unrealized Loss Position Unrealized Loss - Total Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss Outside United States Non-US [Member] Net profit in connection with commercialization Net Profit In Connection With Commercialization [Member] Net Profit In Connection With Commercialization [Member] Praluent, Kevzara, and Dupixent Praluent, Kevzara, and Dupixent [Member] [Member] Praluent, Kevzara, and Dupixent [Member] [Member] Annual funding maximum of research activities per amended agreement Annual funding maximum of research activities per amended agreement The maximum annual amount of funding for research activities through 2017 per the amended agreement. Percentage of Trial Costs borne by collaborating party Percentage of Trial Costs borne by collaborating party The percentage of subsequent Shared Phase 3 Trial costs borne by the collaborating party upon receipt of the first positive Phase 3 trial results for a co-developed drug candidate. Percentage of Trial Costs borne by entity Percentage of Trial Costs borne by entity The percentage of subsequent Shared Phase 3 Trial costs borne by the Company upon receipt of the first positive Phase 3 trial results for a co-developed drug candidate. Income Tax Disclosure [Abstract] Operating Loss Carryforwards [Table] Operating Loss Carryforwards [Table] Income Tax Authority [Axis] Income Tax Authority [Axis] Income Tax Authority [Domain] Income Tax Authority [Domain] Domestic Tax Authority [Member] Domestic Tax Authority [Member] Operating Loss Carryforwards [Line Items] Operating Loss Carryforwards [Line Items] Total income tax expense (benefit) Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Provisional charge for re-measurement of U.S. deferred tax assets due to US Tax Reform Provisional charge for re-measurement of U.S. deferred tax assets due to US Tax Reform Provisional charge recorded during Q4 2017 for the remeasurement of U.S. deferred tax assets upon the enactment of Tax Cut and Jobs Act Schedule of New Accounting Pronouncements and Changes in Accounting Principles Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Restrictions on Cash and Cash Equivalents [Table Text Block] Restrictions on Cash and Cash Equivalents [Table Text Block] Income Taxes Income Tax Disclosure [Text Block] Revenue recognition, milestone method, revenue recognized Revenue Recognition, Milestone Method, Revenue Recognized Aggregate future development milestone payments the Company is eligible to receive Aggregate future development milestone payments the Company is eligible to receive Aggregate future development milestone payments the Company is eligible to receive. Collaborative arrangement, additional eligible aggregate payments Collaborative Arrangement, Additional Eligible Aggregate Payments The aggregate amount of additional payments the Company is entitled to receive upon the achievement of specified annual net sales amounts. Interim Financial Statements Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Loss Contingency [Abstract] Loss Contingency [Abstract] Attorneys' fees Legal Fees Loss contingency, damages sought, per unit produced Loss Contingency, Damages Sought, per unit produced. Loss Contingency, Damages Sought, per unit produced. Loss contingency, damages sought, amount Loss Contingency, Damages Sought, Value Marketable securities, realized gain (loss) Marketable Securities, Realized Gain (Loss) Net unrealized gain on securities Equity Securities, FV-NI, Unrealized Gain (Loss) Legal Matters Legal Costs, Policy [Policy Text Block] New Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Accounts receivable, net (recorded within Prepaid expenses and other current assets) Maturities within one year Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Fair Value Maturities after one year through five years Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Fair Value Total Preferred stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Preferred stock, shares authorized (in shares) Preferred Stock, Shares Authorized Preferred stock, issued (in shares) Preferred Stock, Shares Issued Preferred stock, outstanding (in shares) Preferred Stock, Shares Outstanding Common Stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common Stock, shares authorized (in shares) Common Stock, Shares Authorized Common Stock, shares issued (in shares) Common Stock, Shares, Issued Common Stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Treasury stock, outstanding (in shares) Treasury Stock, Shares Raw materials Inventory, Raw Materials, Net of Reserves Work-in-process Inventory, Work in Process, Net of Reserves Finished goods Inventory, Finished Goods, Net of Reserves Deferred costs Other Inventory, Net of Reserves Total Inventories