Maturities within one year Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Business Acquisition [Axis] Business Acquisition [Axis] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Schedule of Cash and Cash Equivalents Schedule of Cash and Cash Equivalents [Table Text Block] Deferred tax assets Deferred Income Tax Assets, Net Fair Value and Unrealized Losses of Marketable Securities Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block] Entity Address, Postal Zip Code Entity Address, Postal Zip Code November 2021 Share Repurchase Program Share Repurchase Program, November 2021 [Member] Share Repurchase Program, November 2021 Preferred Stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Number of IPR filed Number of Inter Parties Review (IPR) Petitions Filed Number of Inter Parties Review (IPR) Petitions Filed Debt Instrument [Axis] Debt Instrument [Axis] Sales Milestone Four Sales Milestone Four [Member] Sales Milestone Four Finance lease liability Finance Lease, Liability Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Revolving credit facility Line of Credit Facility, Maximum Borrowing Capacity Receivable [Domain] Receivable [Domain] '226 and '992 Patents '226 Patent And '992 Patent [Member] '226 Patent And '992 Patent Additional paid-in capital Additional Paid in Capital Financial Instruments [Domain] Financial Instruments [Domain] Statistical Measurement [Domain] Statistical Measurement [Domain] Interest rate Debt Instrument, Interest Rate, Stated Percentage Sales or maturities of marketable and other securities Proceeds from Sale and Maturity of Marketable Securities Legal Matters Legal Matters and Contingencies [Text Block] Other non-cash items, net Other Noncash Income (Expense) Cost of treasury stock received Treasury Stock, Value, Acquired, Cost Method Net income Net income Net income - basic and diluted Net Income (Loss) Attributable to Parent Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Leases Lessee, Finance Leases [Text Block] Maturities after one year through five years Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, after Year One Through Five Antidilutive weighted average number of shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Subsequent Event Type [Axis] Subsequent Event Type [Axis] Share Repurchase Program [Domain] Share Repurchase Program [Domain] Equity Component [Domain] Equity Component [Domain] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Sales-based milestone earned Sales-Based Milestone Earned [Member] Sales-Based Milestone Earned Other operating income Other Operating Income (Expense) [Member] Leases Lessee, Operating Leases [Text Block] McKesson Corporation McKesson Corporation [Member] McKesson Corporation [Member] Sanofi Collaboration Agreement, Amended and Restated Immuno-oncology License and Collaboration Agreement Sanofi Collaboration Agreement, Amended and Restated Immuno-oncology License and Collaboration Agreement [Member] Sanofi Collaboration Agreement, Amended and Restated Immuno-oncology License and Collaboration Agreement Evkeeza Evkeeza [Member] Evkeeza Lessee, Lease, Description [Line Items] Lessee, Lease, Description [Line Items] Fair Value Total Available-for-sale debt securities Debt Securities, Available-for-Sale Libtayo LIBTAYO Net Product Sales [Member] LIBTAYO Net Product Sales [Member] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Entity Address, State or Province Entity Address, State or Province Level 1 Fair Value, Inputs, Level 1 [Member] Reimbursement for manufacturing of ex-U.S. commercial supplies Reimbursement For Manufacturing Of ex-Commercial Supplies [Member] Reimbursement For Manufacturing Of ex-Commercial Supplies Award Type [Axis] Award Type [Axis] 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. Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Regeneron's share of profits in connection with commercialization of EYLEA outside the United States Net Profit In Connection With Commercialization [Member] Net Profit In Connection With Commercialization [Member] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Available-for-sale Debt Securities Debt Securities, Available-for-Sale [Table Text Block] Other liabilities Other Liabilities Issuance/distribution of Common Stock for 401(k) Savings Plan Stock Issued/Distributed During Period, Value, Employee Benefit Plan Stock Issued/Distributed During Period, Value, Employee Benefit Plan Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Expenses: Costs and Expenses [Abstract] Legal Entity [Axis] Legal Entity [Axis] Long-term debt Long-Term Debt, Excluding Current Maturities Certificates of deposit Certificates of deposit Certificates of Deposit [Member] Total liabilities Liabilities Geographical [Axis] Geographical [Axis] Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Revolving Credit Facility Revolving Credit Facility [Member] Preferred Stock, shares issued (in shares) Preferred Stock, Shares Issued Document Type Document Type Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Percentage of trial costs required to be funded by collaborating party Percentage of Trial Costs Required To Be Funded By Collaborating Party Percentage of Trial Costs Required To Be Funded By Collaborating Party Debt Debt Disclosure [Text Block] Product and Service [Domain] Product and Service [Domain] Entity Shell Company Entity Shell Company Classification of Investment [Axis] Classification of Investment [Axis] This element represents the general categories of investments, which may be classified as Unrestricted or Restricted. Concentration Risk [Table] Concentration Risk [Table] Financial Instrument [Axis] Financial Instrument [Axis] Other Other Collaboration Agreements [Member] Other Collaboration Agreements [Member] Besse Medical, a subsidiary of AmerisourceBergen Corporation Besse Medical [Member] Besse Medical [Member] Subsequent Event Subsequent Event [Member] Schedule of accounts receivable and deferred revenue information Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block] Document Period End Date Document Period End Date Sovereign bonds Sovereign bonds Sovereign Debt Securities [Member] Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-Sale [Table] Net assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Total assets Assets Debt Disclosure [Abstract] Debt Disclosure [Abstract] Earnings Per Share [Abstract] Earnings Per Share [Abstract] Income Statement Location [Axis] Income Statement Location [Axis] 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 Levels Of Twelve Month Sales At Which Sales Milestone Payments Would Be Received Equity securities Equity Securities, FV-NI, Current Antidilutive Securities [Axis] Antidilutive Securities [Axis] Trade accounts receivable Trade Accounts Receivable [Member] Accrued expenses and other current liabilities Accrued Liabilities, Current Net cash used in financing activities Net Cash Provided by (Used in) Financing Activities Long-term debt fair value Long-Term Debt, Fair Value Share repurchase program, authorized amount Stock Repurchase Program, Authorized Amount Interest expense Interest Expense, Debt Line of Credit Line of Credit [Member] Asset-backed securities Asset-Backed Securities [Member] Income before income taxes Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Stockholders' Equity Attributable to Parent [Abstract] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Net Income Per Share Earnings Per Share [Text Block] Customer [Axis] Customer [Axis] Finance lease liabilities Finance Lease, Liability, Noncurrent Sanofi Sanofi [Member] Sanofi Award Type [Domain] Award Type [Domain] Unrealized Loss - Total Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss Roche Collaboration Agreement Roche Collaboration Agreement [Member] Roche Collaboration Agreement Entity Registrant Name Entity Registrant Name Total adjustments Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities Entity Address, City or Town Entity Address, City or Town Amounts recognized in connection with up-front payments received Amounts Recognized In Connection With Up-Front Payments [Member] Amounts Recognized In Connection With Up-Front Payments [Member] Leases [Abstract] Leases [Abstract] Legal Matters Legal Costs, Policy [Policy Text Block] Minimum Minimum [Member] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Entity Emerging Growth Company Entity Emerging Growth Company Reimbursement of research and development expenses Reimbursement of research and development expenses Reimbursement Of Research And Development Expenses [Member] Reimbursement Of Research And Development Expenses [Member] Common Stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Inventory write-offs and reserves Inventory Write-down Raw materials Inventory, Raw Materials, Net of Reserves Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Treasury Stock Treasury Stock, Common [Member] Fair Value Measurements Fair Value Disclosures [Text Block] Trading Symbol Trading Symbol Entity File Number Entity File Number Beginning Balance, treasury stock (in shares) Ending Balance, treasury stock (in shares) Treasury Stock, Common, Shares Reimbursement of commercialization-related expenses Reimbursement Of Commercialization-Related Expenses [Member] Reimbursement Of Commercialization-Related Expenses Deferred revenue Contract with Customer, Liability, Noncurrent Research and development Research and Development Expense Entity Information [Line Items] Entity Information [Line Items] Effective income tax rate Effective Income Tax Rate Reconciliation, Percent Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] January 2021 Share Repurchase Program Share Repurchase Program, January 2021 [Member] Share Repurchase Program, January 2021 Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Concentration risk, percentage Concentration Risk, Percentage Unrealized gain on cash flow hedges Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] (Decrease) increase in accounts payable, accrued expenses, and other liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Income Taxes Income Tax Disclosure [Text Block] Finished goods Inventory, Finished Goods, Net of Reserves U.S. government US Government [Member] US Government Credit Facility [Domain] Credit Facility [Domain] Fair Value - 12 Months or Greater Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer Net income per share - basic (in dollars per share) Earnings Per Share, Basic Restrictions on Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Counterparty Name [Domain] Counterparty Name [Domain] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Total stockholders' equity Beginning Balance Ending Balance Stockholders' Equity Attributable to Parent Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Apotex Inc. Apotex Inc. [Member] Apotex Inc. Entity Interactive Data Current Entity Interactive Data Current Changes in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Retained Earnings Retained Earnings [Member] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Common Stock Common Stock Common Stock Common Stock [Member] Receivable Type [Axis] Receivable Type [Axis] Issuance of Common Stock for equity awards granted under long-term incentive plans Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Project [Domain] Project [Domain] Cost of goods sold Cost Of Goods Sold [Member] Cost Of Goods Sold Repurchases of Common Stock Payments for Repurchase of Common Stock Class of Stock [Axis] Class of Stock [Axis] Statement [Table] Statement [Table] Regeneron's obligation for its share of Sanofi commercial expenses Regeneron's Share Of Commercial Expenses [Member] Regeneron's Share Of Commercial Expenses Sanofi Collaboration Agreement, Antibody Sanofi Collaboration Agreement, Antibody [Member] Sanofi Collaboration Agreement, Antibody [Member] Marketable securities Marketable Securities, Noncurrent Document Quarterly Report Document Quarterly Report Finance lease, option to extend Lessee, Finance Lease, Option to Extend Current assets: Assets, Current [Abstract] Schedule of Shares Repurchased Class of Treasury Stock [Table Text Block] Laboratory and Office Facilities Laboratory and Office Facilities [Member] Laboratory and Office Facilities Statistical Measurement [Axis] Statistical Measurement [Axis] Treasury stock, shares acquired (in shares) Treasury Stock, Shares, Acquired Retained earnings Retained Earnings (Accumulated Deficit) Accounts receivable, net Accounts Receivable, after Allowance for Credit Loss, Current Purchases of marketable and other securities Payments to Acquire Marketable Securities U.S. government and government agency obligations U.S. government and government agency obligations U.S. government and government agency obligations US Treasury and Government [Member] Equity Components [Axis] Equity Components [Axis] Measured on a recurring basis Fair Value, Recurring [Member] Fair Value - Less than 12 Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months Document Fiscal Year Focus Document Fiscal Year Focus Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Statement [Line Items] Statement [Line Items] Total other income (expense) Nonoperating Income (Expense) EYLEA EYLEA Aflibercept Injection [Member] EYLEA Aflibercept Injection Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Selling, general, and administrative Selling, General and Administrative Expense Loss Contingencies [Table] Loss Contingencies [Table] Unrealized Losses Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Loss, before Tax Net product sales Product [Member] Sales Milestones [Axis] Sales Milestones [Axis] Sales Milestones Repurchases of Common Stock Stock Repurchased During Period, Value Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Capital expenditures Payments to Acquire Productive Assets Document Transition Report Document Transition Report Local Phone Number Local Phone Number Income from operations Operating Income (Loss) Increase in inventories Increase (Decrease) in Inventories Number of ex parte reexamination requests Loss Contingency, Ex Parte Reexamination, Filed, Number Loss Contingency, Ex Parte Reexamination, Filed, Number Securities owned not readily marketable Equity Securities without Readily Determinable Fair Value, Amount Increase in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Accrued expenses and other current liabilities Accrued Liabilities and Other Liabilities Common Stock, shares outstanding (in shares) Beginning Balance (in shares) Ending Balance (in shares) Common Stock, Shares, Outstanding Treasury Stock (in shares) Treasury Stock, Shares Long-Lived Tangible Asset [Axis] Long-Lived Tangible Asset [Axis] Repurchases of Common Stock (in shares) Stock Repurchased During Period, Shares 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] Unrestricted Unrestricted [Member] Investments whose use is not restricted in whole or in part, by contractual agreements or regulatory requirements. Income tax expense Income Tax Expense (Benefit) Geographical [Domain] Geographical [Domain] Preferred Stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Statements of Operations Income Statement [Abstract] Additional Paid-in Capital Additional Paid-in Capital [Member] Document Fiscal Period Focus Document Fiscal Period Focus Cost of goods, collaboration and contract manufacturing Cost of Goods and Services Sold Weighted average shares outstanding - diluted (in shares) Weighted average shares - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Schedule of Inventory, Current Schedule of Inventory, Current [Table Text Block] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-Sale [Line Items] Total marketable securities Marketable Securities Regeneron's share of profits (losses) in connection with commercialization Share Of Profit (Losses) In Connection With Commercialization [Member] Share Of Profit (Losses) In Connection With Commercialization [Member] Common stock Common Stock, Value, Issued Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Regeneron's obligation for its share of Sanofi research and development expenses Regeneron's obligation for its share of Bayer research and development expenses Regeneron's Share Of Research And Development Expenses [Member] Regeneron's Share Of Research And Development Expenses [Member] Restricted Restricted [Member] Restricted [Member] Senior Unsecured Notes Senior Notes [Member] Other operating (income) expense, net Other Operating Income (Expense), Net Antidilutive Securities Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Preferred Stock, shares authorized (in shares) Preferred Stock, Shares Authorized Cash, cash equivalents, and restricted cash at beginning of period Cash, cash equivalents, and restricted cash at end of period Total cash, cash equivalents, and restricted cash shown in the Condensed Consolidated Statement of Cash Flows Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Current liabilities: Liabilities, Current [Abstract] Common Stock, shares issued (in shares) Common Stock, Shares, Issued Concentration Risk [Line Items] Concentration Risk [Line Items] Deferred revenue Contract with Customer, Liability, Current Accrued capital expenditures Capital Expenditures Incurred but Not yet Paid Income Statement Location [Domain] Income Statement Location [Domain] Finance lease liabilities Finance Lease, Liability, Current 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] Fair Value - Total Debt Securities, Available-for-Sale, Unrealized Loss Position Amendment Flag Amendment Flag Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Debt, principal amount Debt Instrument, Face Amount Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Revenue, remaining performance obligation, variable consideration amount Revenue, Remaining Performance Obligation, Variable Consideration Amount Revenue, Remaining Performance Obligation, Variable Consideration Amount Cost of collaboration and contract manufacturing Collaboration and Contract Manufacturing [Member] Collaboration and Contract Manufacturing [Member] Unrealized Gains Debt Securities, Available-for-Sale, Accumulated Gross Unrealized Gain, before Tax Entity Current Reporting Status Entity Current Reporting Status Other noncurrent assets Other Assets, Noncurrent Depreciation and amortization Depreciation, Depletion and Amortization Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Project [Axis] Project [Axis] Counterparty Name [Axis] Counterparty Name [Axis] One-time payment in connection with change in Japan arrangement One-time Payment in Connection With Change in Japan Arrangement [Member] One-time Payment in Connection With Change in Japan Arrangement 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. 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Checkmate Pharmaceuticals, Inc. [Member] Checkmate Pharmaceuticals, Inc. Statements of Comprehensive Income Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Marketable Securities, Based on Contractual Maturity Dates Investments Classified by Contractual Maturity Date [Table Text Block] Entity Filer Category Entity Filer Category Proceeds from issuance of Common Stock Proceeds from Issuance of Common Stock Weighted average shares outstanding - basic (in shares) Weighted average shares - basic (in shares) Weighted Average Number of Shares Outstanding, Basic REGEN-COV REGEN-COV [Member] REGEN-COV Up-front payment to collaborating party Up-Front Payment to Collaborating Party Up-Front Payment to Collaborating Party UNITED STATES UNITED STATES Security Exchange Name Security Exchange Name Preferred Stock, par value $.01 per share; 30.0 shares authorized; issued and outstanding - none Preferred Stock, Value, Issued Restricted stock awards and restricted stock units Restricted Stock [Member] Summary of Issued Senior Unsecured Notes Schedule of Debt [Table Text Block] Reimbursement for manufacturing of commercial supplies Reimbursement for manufacturing of ex-U.S. commercial supplies Reimbursement For Manufacturing Of Commercial Supplies [Member] Reimbursement For Manufacturing Of Commercial Supplies [Member] Revenues Revenue milestones Revenue from Contract with Customer, Excluding Assessed Tax Corporate bonds Corporate bonds Corporate bonds Corporate Bond Securities [Member] Percentage of share of profits used to reimburse collaborating party for trial costs Percentage of Share of Profits Used to Reimburse Collaborating Party for Trial Costs Percentage of Share of Profits Used to Reimburse Collaborating Party for Trial Costs Cover [Abstract] Cover [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Work-in-process Inventory, Work in Process, Net of Reserves Deferred taxes Increase (Decrease) in Deferred Income Taxes Losses (gains) on marketable and other securities, net Marketable and Other Securities, Gain (Loss) Marketable and Other Securities, Gain (Loss) Product Sales Revenue from Contract with Customer [Text Block] 1.750% Senior Notes due September 2030 Senior Unsecured Notes Due 2030 [Member] Senior Unsecured Notes Due 2030 Collaboration revenue Collaboration Revenue [Member] Collaboration Revenue Classification of Investment [Domain] Classification of Investment [Domain] Provides general categories of investments for which information is required or determined to be disclosed. Payments in connection with Common Stock tendered for employee tax obligations Payment, Tax Withholding, Share-Based Payment Arrangement Total liabilities and stockholders' equity Liabilities and Equity Praluent Praluent Net Product Sales [Member] Praluent Net Product Sales Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] 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. Remaining authorized repurchase amount Stock Repurchase Program, Remaining Authorized Repurchase Amount Effect of dilutive securities (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-Based Payment Arrangements Outside United States Non-US [Member] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Asset acquisition, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired Level 2 Fair Value, Inputs, Level 2 [Member] Current Fiscal Year End Date Current Fiscal Year End Date Marketable securities Marketable Securities, Current Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Net income per share - diluted (in dollars per share) Earnings Per Share, Diluted Sales Milestones [Domain] Sales Milestones [Domain] Sales Milestones [Domain] Bayer Bayer Collaboration Agreement [Member] Bayer Collaboration Agreement [Member] Stock-based compensation charges APIC, Share-Based Payment Arrangement, Increase for Cost Recognition Concentration Risk Type [Axis] Concentration Risk Type [Axis] Total current liabilities Liabilities, Current Deferred costs Other Inventory, Net of Reserves Celltrion, Inc. Celltrion, Inc. [Member] Celltrion, Inc. Customer concentration risk Customer Concentration Risk [Member] Regulatory Milestone Regulatory Milestone [Member] Regulatory Milestone Accounts payable Accounts Payable Share Repurchase Program [Axis] Share Repurchase Program [Axis] Remaining performance obligation Revenue, Remaining Performance Obligation, Amount Other income (expense): Nonoperating Income (Expense) [Abstract] Net unrealized gain (loss) on securities Equity Securities, FV-NI, Unrealized Gain (Loss) Entity Address, Address Line One Entity Address, Address Line One Deferred revenue Contract with Customer, Liability Product and Service [Axis] Product and Service [Axis] Class of Stock [Domain] Class of Stock [Domain] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Interest expense Interest Expense Available-for-sale debt securities: Debt Securities, Available-for-Sale [Abstract] Credit Facility [Axis] Credit Facility [Axis] Unrealized loss on debt securities OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Inventories Inventory Disclosure [Text Block] Equity [Abstract] Equity [Abstract] Schedule of Capital Leased Assets [Table] Schedule of Capital Leased Assets [Table] Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] Entity Tax Identification Number Entity Tax Identification Number Schedule of product sales Schedule of collaborative revenue Disaggregation of Revenue [Table Text Block] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] '338 Patent And '069 Patent '338 Patent And '069 Patent [Member] '338 Patent And '069 Patent Common Stock tendered upon exercise of stock options and vesting of restricted stock for employee tax obligations (in shares) Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Net increase (decrease) in cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Commercial paper Commercial paper Commercial Paper [Member] Entity Central Index Key Entity Central Index Key Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Measurement Frequency [Axis] Measurement Frequency [Axis] Common Stock tendered upon exercise of stock options and vesting of restricted stock for employee tax obligations Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation Collaboration, License, and Other Agreements Collaborative Arrangement Disclosure [Text Block] Acquisition, consideration transferred Business Combination, Consideration Transferred Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Entity [Domain] Entity [Domain] City Area Code City Area Code ASSETS Assets [Abstract] Long-term Debt, Type [Domain] Long-Term Debt, Type [Domain] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Sanofi Collaboration Agreement, Immuno-oncology Sanofi Collaboration Agreement, Immuno-oncology Sanofi Collaboration Agreement, Immuno-oncology Sanofi Collaboration Agreement, Immuno-oncology [Member] Sanofi Collaboration Agreement, Immuno-oncology [Member] Regeneron's obligation for Sanofi's share of Libtayo U.S. gross profits Sanofi's Share of Libtayo U.S. Gross Profits [Member] Sanofi's Share of Libtayo U.S. Gross Profits [Member] Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Acquired in-process research and development in connection with asset acquisition Research and Development in Process Stock-based compensation expense Share-Based Payment Arrangement, Noncash Expense Other noncurrent liabilities Other Liabilities, Noncurrent Acquired in-process research and development Acquired In-Process Research and Development Acquired In-Process Research and Development Research and development expense Research and Development Expense [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Basic and Diluted Net Income (Loss) Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Customer [Domain] Customer [Domain]