Leases [Abstract] Remaining lease term (in years) Finance Lease, Remaining Lease Term Finance Lease, Remaining Lease Term Discount rate Lessee, Finance Lease, Discount Rate 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] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Increase as a result of payment received from Sanofi 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 From Prior Period Contract With Customer, Liability, Revenue Recognized From Prior Period Revenue recognized that was added to deferred revenue during the period Contract With Customer, Liability, Revenue Recognized In Current Period Contract With Customer, Liability, Revenue Recognized In Current Period Finance lease, term of contract Lessee, Finance Lease, Term of Contract Finance lease, extension option Lessee, Finance Lease, Renewal Term Property, plant, and equipment, at cost Capital Leased Assets, Gross Accumulated amortization Capital Leases, Net Investment in Direct Financing Leases, Accumulated Amortization Sanofi Collaboration Agreement, Antibody Sanofi Collaboration Agreement, Antibody [Member] Sanofi Collaboration Agreement, Antibody [Member] Increase (decrease) in deferred revenue Revenues [Abstract] Schedule of product sales Disaggregation of Revenue [Table Text Block] 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. Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Outside United States Non-US [Member] Bayer Bayer Collaboration Agreement [Member] Bayer Collaboration Agreement [Member] Product and Service [Axis] Product and Service [Axis] Product and Service [Domain] Product and Service [Domain] Product and service, other Product and Service, Other [Member] Net profit in connection with commercialization Net Profit In Connection With Commercialization [Member] Net Profit In Connection With Commercialization [Member] Reimbursement of Regeneron research and development expenses Reimbursement Of Research And Development Expenses [Member] Reimbursement Of Research And Development Expenses [Member] Other Other [Member] Other [Member] Revenues Revenue from Contract with Customer, Excluding Assessed Tax Statement of Financial Position [Abstract] Statement [Table] Sanofi Sanofi Collaboration Agreement [Member] Sanofi Collaboration Agreement [Member] Other Other Collaboration Agreements [Member] Other Collaboration Agreements [Member] Class of Stock [Axis] Class of Stock [Domain] Class A Stock Common Class A [Member] Common Stock Common Stock [Member] Statement [Line Items] Statement [Line Items] 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, Related Parties, Current 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 Deferred tax assets Deferred Income Tax Assets, Net Other noncurrent assets Other Assets, Noncurrent Total assets Assets LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] Current liabilities: Liabilities, Current [Abstract] Accounts payable Accounts Payable Accrued expenses and other current liabilities Accrued Liabilities and Other Liabilities Deferred revenue, current Contract with Customer, Liability, Current Total current liabilities Liabilities, Current Finance lease liabilities Finance Lease, Liability, Noncurrent Finance lease liabilities Capital and facility lease obligations, noncurrent Represents the noncurrent portion of a lease liability Deferred revenue, noncurrent Contract with Customer, Liability, Noncurrent Other noncurrent liabilities Other Liabilities, Noncurrent Total liabilities 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 Retained earnings Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax Treasury Stock, at cost; 4,046,627 shares in 2019 and 3,990,021 shares in 2018 Treasury Stock, Value Total stockholders' equity Stockholders' Equity Attributable to Parent Total liabilities and stockholders' equity Liabilities and Equity Supplemental Cash Flow Information [Abstract] 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. Treasury stock, shares acquired Treasury Stock, Shares, Acquired Cost of Treasury stock shares received Treasury Stock, Value, Acquired, Cost Method Accounts receivable Deferred revenue Contract with Customer, Liability Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [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] Sovereign bonds Sovereign Debt Securities [Member] Commercial paper Commercial Paper [Member] Certificates of deposit Certificates of Deposit [Member] 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] 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. Restricted Restricted [Member] Restricted [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] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] 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] Available-for-sale debt securities: Debt Securities, Available-for-sale Equity securities Equity Securities, FV-NI Total marketable securities Marketable Securities Statement of Comprehensive Income [Abstract] Statement [Table] Product Product [Member] Collaboration and contract manufacturing Collaboration and Contract Manufacturing [Member] Collaboration and Contract Manufacturing [Member] 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 Operating Income (Loss) 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 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 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 Weighted average shares outstanding - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Weighted average shares - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted 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 debt securities Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, after Tax Unrealized (loss) 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 Product Sales Product Sales and Concentration Risk [Text Block] Product Sales and Concentration Risk Disclosure [Text Block] Statement of Cash Flows Cash Flow, Supplemental Disclosures [Text Block] Commitments and Contingencies Disclosure [Abstract] Loss Contingencies [Table] Loss Contingencies [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] '165 Patent '165 Patent [Member] '165 Patent [Member] '741 Patent '741 Patent [Member] '741 Patent [Member] '688 Patent '688 Patent [Member] '688 Patent [Member] Litigation Case [Axis] Litigation Case [Axis] Litigation Case [Domain] Litigation Case [Domain] Amgen v.s. Regeneron Amgen v.s. Regeneron [Member] Amgen v.s. Regeneron [Member] Litigation Status [Axis] Litigation Status [Axis] Litigation Status [Domain] Litigation Status [Domain] Pending Litigation Pending Litigation [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Pending claims Loss Contingency, Pending Claims, Number Invalid claims Loss Contingency, Claims Invalid, Number Loss Contingency, Claims Invalid, Number 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 Loss Contingency, Damages Sought, Value Asserted claims Loss Contingency, Claims Asserted, Number Loss Contingency, Claims Asserted, Number Teva Teva Pharmaceuticals Collaboration Agreement [Member] Teva Pharmaceuticals Collaboration Agreement [Member] Up-front payment received Up-front payment received Up-front payment received upon the execution of a collaboration agreement. Revenue, performance obligation amount Revenue, Remaining Performance Obligation, Amount Investments, Debt and Equity Securities [Abstract] 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] Other than temporary impairment losses, investments Other than Temporary Impairment Losses, Investments Securities owned not readily marketable Securities Owned Not Readily Marketable 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] Amended IO Discovery Agreement Amended IO Discovery Agreement [Member] Amended IO Discovery Agreement [Member] Libtayo LIBTAYO Net Product Sales [Member] LIBTAYO Net Product Sales [Member] Aggregate payment received with regards to amendment Aggregate Payment Received With Regards To Amendment Aggregate Payment Received With Regards To Amendment Maximum shares the collaborator could sell (in shares) Maximum shares the collaborator could sell Maximum shares the collaborator could sell through September 30, 2020. 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] Adjustments for New Accounting Pronouncements [Axis] Adjustments for New Accounting Pronouncements [Axis] Type of Adoption [Domain] Type of Adoption [Domain] Accounting Standards Update 2016-02 Accounting Standards Update 2016-02 [Member] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Right-of-use assets Operating Lease, Right-of-Use Asset Net unrealized gain on securities Equity Securities, FV-NI, Unrealized Gain (Loss) Schedule of amounts recognized in the Condensed Consolidated Balance Sheet Lessee, Assets And Liabilities, Finance Lease [Table Text Block] Lessee, Assets And Liabilities, Finance Lease [Table Text Block] Schedule of lease cost and other information Lease, Cost [Table Text Block] Schedule of maturities of lease liabilities Lessee, Operating Lease, Liability, Maturity [Table Text Block] Schedule of maturities of lease liabilities Finance Lease, Liability, Maturity [Table Text Block] Schedule of future minimum noncancelable lease commitments Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Schedule of future minimum noncancelable lease commitments Schedule of Future Minimum Lease Payments for Capital Leases [Table Text Block] Collaboration Agreements Collaborative Arrangement Disclosure [Text Block] Schedule of collaboration revenue Schedule of accounts receivable and deferred revenue information Contract with Customer, Asset and Liability [Table Text Block] Earnings Per Share [Abstract] 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] Net income - basic and diluted Effect of dilutive securities: Incremental Weighted Average Shares Attributable to Dilutive Effect [Abstract] Effect of dilutive securities (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Dilutive potential shares (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Weighted average shares - diluted (in shares) Fair Value Measurements Fair Value Disclosures [Text Block] Net Income Per Share Earnings Per Share [Text Block] Concentration Risk [Table] Concentration Risk [Table] 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] Concentration Risk [Line Items] Concentration Risk [Line Items] Concentration risk, percentage Concentration Risk, Percentage Inventory Disclosure [Abstract] Schedule of Inventory, Current Schedule of Inventory, Current [Table Text Block] 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] Schedule of assets measured at fair value on a recurring basis Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block] Amortization of right-of-use assets Finance Lease, Right-of-Use Asset, Amortization Interest on lease liabilities Finance Lease, Interest Expense Finance lease costs Finance Lease, Cost Finance Lease, Cost 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] Praluent, Kevzara, and Dupixent Praluent, Kevzara, and Dupixent [Member] [Member] Praluent, Kevzara, and Dupixent [Member] [Member] 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. 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 Leases Lessee, Finance Leases [Text Block] Leases Lessee, Operating Leases [Text Block] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] 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 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 Accounting Policies [Abstract] Leases Lessee, Leases [Policy Text Block] Legal Matters Legal Costs, Policy [Policy Text Block] New Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Income Tax Disclosure [Abstract] Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Interim Financial Statements Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Legal Matters Legal Matters and Contingencies [Text Block] Document And Entity Information [Abstract] -- None. No documentation exists for this element. -- Entities [Table] 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 Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Inventories Inventory Disclosure [Text Block] Recently Issued Accounting Standards Description of New Accounting Pronouncements Not yet Adopted [Text Block] Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [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. Income Taxes Income Tax Disclosure [Text Block] 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 Weighted average number of shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 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 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 Statement of Cash Flows [Abstract] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income 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) decrease in Sanofi, Bayer, and trade accounts receivable Increase (Decrease) in Accounts Receivable Increase in inventories Increase (Decrease) in Inventories Decrease in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets (Decrease) increase 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 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 Repurchases of Common Stock Payments for Repurchase of Common Stock 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 Operating Leases Operating Lease Liabilities, Payments Due [Abstract] 2019 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2020 Lessee, Operating Lease, Liability, Payments, Due Year Two 2021 Lessee, Operating Lease, Liability, Payments, Due Year Three 2022 Lessee, Operating Lease, Liability, Payments, Due Year Four 2023 Lessee, Operating Lease, Liability, Payments, Due Year Five 2024 Lessee, Operating Lease, Liability, Payments, Due Year Six Lessee, Operating Lease, Liability, Payments, Due Year Six Thereafter Lessee, Operating Lease, Liability, Payments, Due After Year Six Lessee, Operating Lease, Liability, Payments, Due After Year Six Total undiscounted lease payments Lessee, Operating Lease, Liability, Payments, Due Imputed interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Debt financing costs Lessee, Operating Lease, Liability, Debt Financing Costs Lessee, Operating Lease, Liability, Debt Financing Costs Total lease liabilities Operating Lease, Liability, Noncurrent Finance Leases Finance Lease Liabilities, Payments, Due [Abstract] 2019 Finance Lease, Liability, Payments, Remainder of Fiscal Year 2020 Finance Lease, Liability, Payments, Due Year Two 2021 Finance Lease, Liability, Payments, Due Year Three 2022 Finance Lease, Liability, Payments, Due Year Four 2023 Finance Lease, Liability, Payments, Due Year Five 2024 Finance Lease, Liability, Payments, Due Year Six Finance Lease, Liability, Payments, Due Year Six Thereafter Finance Lease, Liability, Payments, Due After Year Six Finance Lease, Liability, Payments, Due After Year Six Total undiscounted lease payments Finance Lease, Liability, Payments, Due Imputed interest Finance Lease, Liability, Undiscounted Excess Amount Debt financing costs Lessee, Finance Lease, Liability, Debt Financing Costs Lessee, Finance Lease, Liability, Debt Financing Costs Operating Leases Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2019 Operating Leases, Future Minimum Payments, Remainder of Fiscal Year 2020 Operating Leases, Future Minimum Payments, Due in Two Years 2021 Operating Leases, Future Minimum Payments, Due in Three Years 2022 Operating Leases, Future Minimum Payments, Due in Four Years 2023 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Operating Leases Operating Leases, Future Minimum Payments Due Capital and Facility Lease Obligations Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2019 Capital Leases, Future Minimum Payments, Remainder of Fiscal Year 2020 Capital Leases, Future Minimum Payments Due in Two Years 2021 Capital Leases, Future Minimum Payments Due in Three Years 2022 Capital Leases, Future Minimum Payments Due in Four Years 2023 Capital Leases, Future Minimum Payments Due in Five Years Thereafter Capital Leases, Future Minimum Payments Due Thereafter Capital and Facility Lease Obligations Capital Leases, Future Minimum Payments Due 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] Research Collaboration and Licensing Arrangements [Table] Research Collaboration and Licensing Arrangements [Table] -- None. No documentation exists for this element. -- Alnylam Alnylam Pharmaceuticals, Inc. Collaboration Agreement [Member] Alnylam Pharmaceuticals, Inc. Collaboration Agreement [Member] Alnylam Stock Purchase Agreement Alnylam Pharmaceuticals, Inc. Stock Purchase Agreement [Member] Alnylam Pharmaceuticals, Inc. Stock Purchase Agreement [Member] Research Collaboration and Licensing Arrangements [Line Items] Research Collaboration and Licensing Arrangements [Line Items] Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. Upfront payment made Upfront Payment Made Upfront payment made under a collaboration agreement Additional payment eligible to be made Collaborative Arrangement, Additional Payment Eligible, Milestone Collaborative Arrangement, Additional Payment Eligible, Milestone Initial research term Initial Research Term Initial Research Term Potential extension of research term Potential Extension Of Research Term Potential Extension Of Research Term Extension of research term fee Extension Of Research Term Fee Extension Of Research Term Fee Cash consideration Expected Payments To Be Made To Acquire Equity Within A Collaboration Agreement Expected Payments To Be Made To Acquire Equity Within A Collaboration Agreement Statement of Stockholders' Equity [Abstract] 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] Accounting Standards Update 2014-09 And 2016-01 Accounting Standards Update 2014-09 And 2016-01 [Member] Accounting Standards Update 2014-09 And 2016-01 [Member] Accounting Standards Update 2016-01 Accounting Standards Update 2016-01 [Member] Class of Stock [Axis] Class of Stock [Domain] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Additional Paid-in Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Treasury Stock Treasury Stock [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning Balance (in shares) Shares, Outstanding Beginning Balance Issuance of Common Stock in connection with exercise of stock options (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Issuance of Common Stock in connection with exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Common Stock tendered upon exercise of stock options and vesting of restricted stock in connection with employee tax obligations Adjustments Related to Tax Withholding for Share-based Compensation Issuance of Common Stock in connection with Company 401(k) Savings Plan contribution (in shares) Stock Issued During Period, Shares, Employee Benefit Plan Issuance of Common Stock in connection with Company 401(k) Savings Plan Stock Issued During Period, Value, Employee Benefit Plan Repurchases of Common Stock from Sanofi (in shares) Repurchases of Common Stock from Sanofi Stock-based compensation charges Adjustments to Additional Paid in Capital, Share-based Compensation, Requisite Service Period Recognition Cumulative-effect adjustment upon adoption of new accounting standards Cumulative Effect of New Accounting Principle in Period of Adoption Other comprehensive loss, net of tax Other Comprehensive Income (Loss), Net of Tax Ending Balance (in shares) Ending Balance Finance lease assets Finance Lease, Right-of-Use Asset Accumulated amortization Finance Lease, Right-of-Use Asset, Accumulated Amortization Finance Lease, Right-of-Use Asset, Accumulated Amortization 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 Accounts receivable (recorded within Prepaid expenses and other current assets) 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 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. Restrictions on Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block]