Restatement [Axis] Revision of Prior Period [Axis] Other (expense) income, net Other Nonoperating Income (Expense) Statements of Comprehensive Income Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract] Conversion of Class A Stock to Common Stock (in shares) Stock Issued During Period, Shares, Conversion of Units Increase in accounts payable, accrued expenses, and other liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities Treasury Stock Treasury Stock [Member] Bridge Facility Bridge Loan [Member] Marketable Securities Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Shares purchase price Investment Owned, at Cost Sales or maturities of marketable and other securities Proceeds from Sale and Maturity of Marketable Securities Royalty percentage to be received on net product sales outside of the United States Royalty Percentage To Be Received On Net Product Sales Outside Of United States Royalty Percentage To Be Received On Net Product Sales Outside Of United States 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 Statistical Measurement [Domain] Statistical Measurement [Domain] LIABILITIES AND STOCKHOLDERS' EQUITY LIABILITIES AND STOCKHOLDERS' EQUITY Liabilities and Equity [Abstract] Current Fiscal Year End Date Current Fiscal Year End Date Total adjustments Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities Proceeds from issuance of long-term debt Proceeds from Issuance of Long-term Debt Income from operations Operating Income (Loss) Entity Address, Postal Zip Code Entity Address, Postal Zip Code Conversion of Class A Stock to Common Stock Stock Issued During Period, Value, Conversion of Units Total current liabilities Liabilities, Current '487 Patent '487 Patent [Member] '487 Patent [Member] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] Schedule of Error Corrections and Prior Period Adjustment Restatement [Table] 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 Repurchases of Common Stock Payments for Repurchase of Common Stock ASSETS Assets [Abstract] Issuance of Common Stock for equity awards granted under long-term incentive plans Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Entity Shell Company Entity Shell Company Cover [Abstract] Cover [Abstract] Document Type Document Type Retained earnings Retained Earnings (Accumulated Deficit) Repurchases of Common Stock (in shares) Treasury stock, shares acquired (in shares) Number of shares repurchased (in shares) Treasury Stock, Shares, Acquired McKesson Corporation McKesson Corporation [Member] McKesson Corporation [Member] Legal Matters Legal Matters and Contingencies [Text Block] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Customer [Axis] Customer [Axis] Sales-based milestone earned Sales-Based Milestone [Member] Sales-Based Milestone Beginning Balance (in shares) Ending Balance (in shares) Shares, Outstanding Preferred Stock, $.01 par value; 30,000,000 shares authorized; issued and outstanding - none Preferred Stock, Value, Issued 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] Document Quarterly Report Document Quarterly Report Common Stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Total marketable securities Marketable Securities Other comprehensive income (loss), net of tax: Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Other noncurrent liabilities Other Liabilities, Noncurrent Deferred tax assets Deferred Income Tax Assets, Net Marketable securities Marketable Securities, Current Libtayo LIBTAYO Net Product Sales [Member] LIBTAYO Net Product Sales [Member] Work-in-process Inventory, Work in Process, Net of Reserves Stock-based compensation charges APIC, Share-based Payment Arrangement, Increase for Cost Recognition Inventories Total Inventories Inventory, Net Revenues Revenue from Contract with Customer, Excluding Assessed Tax Measurement Frequency [Domain] Measurement Frequency [Domain] Deferred costs Other Inventory, Net of Reserves 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. Regeneron's net profit in connection with commercialization of EYLEA outside the United States Net Profit In Connection With Commercialization [Member] Net Profit In Connection With Commercialization [Member] Concentration risk, percentage Concentration Risk, Percentage Entity File Number Entity File Number 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] Geographical [Domain] Geographical [Domain] Statement [Line Items] Statement [Line Items] Antidilutive Securities Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Reimbursement of other expenses Other [Member] Other [Member] 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 Deferred taxes Increase (Decrease) in Deferred Income Taxes Class of Stock [Domain] Class of Stock [Domain] Document Fiscal Period Focus Document Fiscal Period Focus Statement [Table] Statement [Table] Statistical Measurement [Axis] Statistical Measurement [Axis] Preferred Stock, shares issued (in shares) Preferred Stock, Shares Issued Other operating (income) expense, net Other Operating Income (Expense), Net Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Number of shares sold (in shares) Sale of Stock, Number of Shares Issued in Transaction Debt Debt Disclosure [Text Block] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] 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. Issuance/distribution of Common Stock in connection with 401(k) Savings Plan (in shares) Stock Issued/Distributed During Period, Shares, Employee Benefit Plan Stock Issued/Distributed During Period, Shares, Employee Benefit Plan Proceeds from issuance of Common Stock Proceeds from Issuance of Common Stock Share Repurchase Program [Domain] Share Repurchase Program [Domain] Basic and Diluted Net Income (Loss) Per Share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Classification of Investment [Axis] Classification of Investment [Axis] This element represents the general categories of investments, which may be classified as Unrestricted or Restricted. Schedule of Shares Repurchased Class of Treasury Stock [Table Text Block] Amendment Flag Amendment Flag Loss contingency, damages sought, per unit produced Loss Contingency, Damages Sought, Per Unit Produced Loss Contingency, Damages Sought, Per Unit Produced Besse Medical, a subsidiary of AmerisourceBergen Corporation Besse Medical [Member] Besse Medical [Member] Other Other Collaboration Agreements [Member] Other Collaboration Agreements [Member] Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Measurement Frequency [Axis] Measurement Frequency [Axis] Other Other Revenue [Member] Other Revenue [Member] Financial Instruments [Domain] Financial Instruments [Domain] Share Repurchase Program Share Repurchase Program [Member] Share Repurchase Program [Member] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Proceeds from bridge loan facility Proceeds from Short-term Debt '165 Patent '165 Patent [Member] '165 Patent [Member] Fair Value - 12 Months or Greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer Senior Unsecured Notes Senior Notes [Member] Statement of Cash Flows Cash Flow, Supplemental Disclosures [Text Block] Accrued capital expenditures Capital Expenditures Incurred but Not yet Paid Product Sales Product Sales and Concentration Risk [Text Block] Product Sales and Concentration Risk Disclosure [Text Block] Geographical [Axis] Geographical [Axis] Local Phone Number Local Phone Number Amortized Cost Basis Debt Securities, Available-for-sale, Amortized Cost Reduction of Selling, general, and administrative expense Reimbursement Of Selling, General And Administrative Expense Reimbursement Of Selling, General And Administrative Expense Invalid claims Loss Contingency, Claims Invalid, Number Loss Contingency, Claims Invalid, Number Unrealized Gains Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Sanofi Sanofi [Member] Sanofi [Member] Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Selling, general, and administrative Selling, General and Administrative Expense Line of Credit Facility [Table] Line of Credit Facility [Table] Entity Current Reporting Status Entity Current Reporting Status 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] Legal Matters Legal Costs, Policy [Policy Text Block] Other noncurrent assets Other Assets, Noncurrent Other liabilities Other Liabilities Marketable securities Marketable Securities, Noncurrent Concentration Risk [Table] Concentration Risk [Table] Total assets Assets Interest expense Interest Expense, Debt Amounts recognized in connection with up-front payments received Amounts recognized in connection with up-front and development milestone payments received Amounts Recognized In Connection With Up-Front Payments [Member] Amounts Recognized In Connection With Up-Front Payments [Member] Unrealized (loss) gain on debt securities OCI, Debt Securities, Available-for-Sale, Unrealized Holding Gain (Loss), before Adjustment, after Tax Antidilutive Securities [Axis] Antidilutive Securities [Axis] Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Entity Small Business Entity Small Business As Previously Reported Previously Reported [Member] Interest expense Interest Expense Depreciation and amortization Depreciation, Depletion and Amortization Entity Filer Category Entity Filer Category Reimbursement of research and development expenses Reimbursement of development expenses Reimbursement Of Research And Development Expenses [Member] Reimbursement Of Research And Development Expenses [Member] Net unrealized gain (loss) on securities Equity Securities, FV-NI, Unrealized Gain (Loss) Product and Service [Axis] Product and Service [Axis] Total liabilities Liabilities Entity Address, City or Town Entity Address, City or Town Investment Type [Axis] Investment Type [Axis] Loss contingency, damages sought Loss Contingency, Damages Sought, Value Reimbursement of commercialization-related expenses Reimbursement Of Commercialization-Related Expenses [Member] Reimbursement Of Commercialization-Related Expenses [Member] Outside United States Non-US [Member] Fair Value - Total Debt Securities, Available-for-sale, Unrealized Loss Position Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Level 1 Fair Value, Inputs, Level 1 [Member] Increase in inventories Increase (Decrease) in Inventories Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Document Fiscal Year Focus Document Fiscal Year Focus Fair Value - Less than 12 Months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months Raw materials Inventory, Raw Materials, Net of Reserves Teva Teva Pharmaceuticals Collaboration Agreement [Member] Teva Pharmaceuticals Collaboration Agreement [Member] 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. Gross Sales Revenue Gross Sales Revenue [Member] Gross Sales Revenue [Member] Debt Instrument [Axis] Debt Instrument [Axis] Additional Paid-in Capital Additional Paid-in Capital [Member] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Class of Stock [Line Items] Class of Stock [Line Items] Repurchases of Common Stock Cost of treasury stock received Total cost of shares received Treasury Stock, Value, Acquired, Cost Method 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] Litigation Case [Axis] Litigation Case [Axis] Revenue from Contract with Customer [Abstract] Revenue from Contract with Customer [Abstract] Common Stock, shares outstanding (in shares) Common Stock, Shares, Outstanding Income Tax Disclosure [Abstract] Income Tax Disclosure [Abstract] Other operating income Other Operating Income Loss Contingency Nature [Axis] Loss Contingency Nature [Axis] Research and development Research and development expense Research and Development Expense Common Stock, shares authorized (in shares) Common Stock, Shares Authorized Concentration Risk Type [Axis] Concentration Risk Type [Axis] Effect of dilutive securities (in shares) Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Document Period End Date Document Period End Date Bridge Facility Bridge Facility [Member] Bridge Facility Entity Registrant Name Entity Registrant Name Estimate of Fair Value Measurement Estimate of Fair Value Measurement [Member] Statements of Operations Income Statement [Abstract] Accumulated Other Comprehensive Income (Loss) AOCI Attributable to Parent [Member] Marketable Securities, Based on Contractual Maturity Dates Investments Classified by Contractual Maturity Date [Table Text Block] Decrease in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Use of Estimates Use of Estimates, Policy [Policy Text Block] Current assets: Assets, Current [Abstract] Sanofi Collaboration Agreement, Antibody Sanofi Collaboration Agreement, Antibody [Member] Sanofi Collaboration Agreement, Antibody [Member] Remaining authorized repurchase amount Stock Repurchase Program, Remaining Authorized Repurchase Amount 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. Unsatisfied obligation Unsatisfied Obligation Unsatisfied Obligation Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Maximum shares the collaborator could sell (in shares) Maximum shares the collaborator could sell Maximum shares the collaborator could sell through September 30, 2020. Preferred Stock, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Adjustments Revision of Prior Period, Adjustment [Member] Entity Tax Identification Number Entity Tax Identification Number Loss contingency accrual Loss Contingency Accrual Upfront payment made for collaboration agreement Collaborative Arrangement, Upfront Payment Made Upfront payment made under a collaboration agreement Cost of collaboration and contract manufacturing Reimbursement Of Other Expenses Reimbursement Of Other Expenses Unrealized Loss - Total Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss Share repurchase program, authorized amount Stock Repurchase Program, Authorized Amount Accounts receivable - Sanofi Accounts receivable, net Accounts receivable, net Accounts Receivable, Related Parties, Current Schedule of product sales Disaggregation of Revenue [Table Text Block] Income before income taxes Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Trading Symbol Trading Symbol Entity Information [Line Items] Entity Information [Line Items] Schedule of assets measured at fair value on a recurring basis Fair Value, Assets Measured on Recurring and Nonrecurring Basis [Table Text Block] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Schedule of Inventory, Current Schedule of Inventory, Current [Table Text Block] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Non-cash compensation expense Share-based Payment Arrangement, Noncash Expense Capital expenditures Payments to Acquire Productive Assets Equity securities Equity Securities, FV-NI Legal Entity [Axis] Legal Entity [Axis] 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. Amgen v.s. Regeneron Amgen v.s. Regeneron [Member] Amgen v.s. Regeneron [Member] Payments in connection with Common Stock tendered for employee tax obligations Payment, Tax Withholding, Share-based Payment Arrangement 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. Available-for-sale Debt Securities Debt Securities, Available-for-sale [Table Text Block] Entity [Domain] Entity [Domain] Increase in deferred revenue Increase (Decrease) in Contract with Customer, Liability Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Unrestricted Unrestricted [Member] Investments whose use is not restricted in whole or in part, by contractual agreements or regulatory requirements. Percentage of research and development costs to be paid by counterparty Percentage Of Research And Developments Costs To Be Paid By Counterparty Percentage Of Research And Developments Costs To Be Paid By Counterparty City Area Code City Area Code Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Cost of goods sold Cost of collaboration and contract manufacturing Cost of goods sold Cost of Goods and Services Sold Fair Value Total Available-for-sale debt securities: Debt Securities, Available-for-sale Total operating expenses Costs and Expenses Equity Components [Axis] Equity Components [Axis] Unrealized gain (loss) on cash flow hedges Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax Title of 12(b) Security Title of 12(b) Security Pending claims Loss Contingency, Pending Claims, Number Restricted stock Restricted Stock [Member] Finished goods Inventory, Finished Goods, Net of Reserves Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Minimum Minimum [Member] Summary of Non-Cash Investing and Financing Activities Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Regeneron's share of profits in connection with commercialization of antibodies Share Of Profit (Losses) In Connection With Commercialization [Member] Share Of Profit (Losses) In Connection With Commercialization [Member] Corporate bonds Corporate bonds Corporate bonds Corporate Bond Securities [Member] UNITED STATES UNITED STATES Restrictions on Cash and Cash Equivalents Restrictions on Cash and Cash Equivalents [Table Text Block] Revenues: Revenues [Abstract] Revenues [Abstract] Fair Value Measurements Fair Value Disclosures [Text Block] Cash flows from operating activities: Net Cash Provided by (Used in) Operating Activities [Abstract] Stockholders' Equity Stockholders' Equity Note Disclosure [Text Block] Fair Value and Unrealized Losses of Marketable Securities Debt Securities, Available-for-sale, Unrealized Loss Position, Fair Value [Table Text Block] 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] Customer [Domain] Customer [Domain] Cumulative Effect, Period of Adoption, Adjustment Cumulative Effect, Period of Adoption, Adjustment [Member] Accounts payable Accounts Payable Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Concentration Risk [Line Items] Concentration Risk [Line Items] Sanofi Sanofi Collaboration Agreement [Member] Sanofi Collaboration Agreement [Member] '741 Patent '741 Patent [Member] '741 Patent [Member] Accounts receivable - trade, net Accounts Receivable, after Allowance for Credit Loss, Current Maximum agreement payments Maximum Transaction Agreement Payments Maximum Transaction Agreement Payments Schedule of Cash and Cash Equivalents Schedule of Cash and Cash Equivalents [Table Text Block] Unrealized Losses Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax Collaboration and contract manufacturing Collaboration and Contract Manufacturing [Member] Collaboration and Contract Manufacturing [Member] Accounts receivable - other Accounts and Financing Receivable, after Allowance for Credit Loss Debt Securities, Available-for-sale [Line Items] Debt Securities, Available-for-sale [Line Items] Maturities within one year Debt Securities, Available-for-Sale, Fair Value, Maturity, Allocated and Single Maturity Date, Year One Unrealized Loss - 12 Months or Greater Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Other income (expense): Nonoperating Income (Expense) [Abstract] Debt, principal amount Debt Instrument, Face Amount Level 2 Fair Value, Inputs, Level 2 [Member] 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. Entities [Table] Entities [Table] Equity [Abstract] Equity [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] Entity Central Index Key Entity Central Index Key Deferred revenue, current Contract with Customer, Liability, Current Entity Emerging Growth Company Entity Emerging Growth Company Schedule of Reclassifications Schedule of Error Corrections and Prior Period Adjustments [Table Text Block] Cumulative Effect, Period of Adoption [Axis] Cumulative Effect, Period of Adoption [Axis] Customer concentration risk Customer Concentration Risk [Member] Repayment of bridge loan facility Repayments of Short-term Debt Weighted average shares outstanding - diluted (in shares) Weighted average shares - diluted (in shares) Weighted Average Number of Shares Outstanding, Diluted Number of claims invalidated Gain Contingency, Claims Invalidated, Number Gain Contingency, Claims Invalidated, Number Litigation Case [Domain] Litigation Case [Domain] Net income per share - basic (in dollars per share) Earnings Per Share, Basic Debt Disclosure [Abstract] Debt Disclosure [Abstract] Percentage of damages company is responsible for Loss Contingency, Percentage Of Damages Responsible For Loss Contingency, Percentage Of Damages Responsible For Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Short-term Debt, Type [Axis] Short-term Debt, Type [Axis] Common stock Common Stock, Value, Issued Praluent Agreement Praluent Cross License And Commercialization Agreement [Member] Praluent Cross License And Commercialization Agreement [Member] Research Collaboration and Licensing Arrangements [Table] Research Collaboration and Licensing Arrangements [Table] -- None. No documentation exists for this element. -- Commercial paper Commercial paper Commercial Paper [Member] 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 Issuance of Common Stock for equity awards granted under long-term incentive plans (in shares) Shares Issued, Shares, Share-based Payment Arrangement, after Forfeiture Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] Collaboration, License, and Other Agreements Collaborative Arrangement Disclosure [Text Block] Cash flows from investing activities: Net Cash Provided by (Used in) Investing Activities [Abstract] Common Stock, shares issued (in shares) Common Stock, Shares, Issued Cash and cash equivalents Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Shares purchased (in shares) Investment Owned, Balance, Shares Litigation Status [Axis] Litigation Status [Axis] Long-term debt Long-term Debt, Excluding Current Maturities Share Repurchase Program [Axis] Share Repurchase Program [Axis] Increase in Sanofi, trade, and other accounts receivable Increase (Decrease) in Accounts Receivable Project [Domain] Project [Domain] Percentage of royalty payment that can be used to offset litigation proceedings Percentage Of Royalty Payment That Can Be Offset Percentage Of Royalty Payment That Can Be Offset Statement of Comprehensive Income [Abstract] Statement of Comprehensive Income [Abstract] Total stockholders' equity Beginning Balance Ending Balance Stockholders' Equity Attributable to Parent Summary of contract balances Contract With Customer and Collaborator Asset And Liability [Table Text Block] Contract With Customer and Collaborator Asset And Liability [Table Text Block] Concentration Risk Type [Domain] Concentration Risk Type [Domain] '631 Patent '631 Patent [Member] '631 Patent Total liabilities and stockholders' equity Liabilities and Equity Loss Contingencies [Line Items] Loss Contingencies [Line Items] Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Income Taxes Income Tax Disclosure [Text Block] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Schedules of Concentration of Risk, by Risk Factor Schedules of Concentration of Risk, by Risk Factor [Table Text Block] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Financial Instrument [Axis] Financial Instrument [Axis] 2050 Notes Senior Unsecured Notes Due 2050 [Member] Senior Unsecured Notes Due 2050 Antidilutive weighted average number of shares (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Other non-cash items, net Other Noncash Income (Expense) Product Product [Member] Equity Component [Domain] Equity Component [Domain] Entity Address, Address Line One Entity Address, Address Line One Property, plant, and equipment, net Property, Plant and Equipment, Net Collaboration Agreements Revenue from Contract with Customer [Policy Text Block] Net income Net income Net income - basic and diluted Net Income (Loss) Attributable to Parent Entity Address, State or Province Entity Address, State or Province Finance lease liabilities Finance Lease, Liability, Noncurrent Changes in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Other liabilities - Sanofi Other Liabilities, Current Inventories Inventory Disclosure [Text Block] Other comprehensive income (loss), net of tax Other Comprehensive Income (Loss), Net of Tax Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Total current assets Assets, Current Earnings Per Share [Abstract] Earnings Per Share [Abstract] Reimbursement for manufacturing of commercial supplies Reimbursement For Manufacturing Of Commercial Supplies [Member] Reimbursement For Manufacturing Of Commercial Supplies [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Intellia Intellia [Member] Intellia Stockholders' equity: Stockholders' Equity Attributable to Parent [Abstract] Stockholders' Equity Attributable to Parent [Abstract] Cash and Cash Equivalents [Abstract] Entity Interactive Data Current Entity Interactive Data Current Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Certificates of deposit Certificates of deposit Certificates of Deposit [Member] 2030 Notes Senior Unsecured Notes Due 2030 [Member] Senior Unsecured Notes Due 2030 Other Transaction Agreement BARDA, Other Transaction Agreement [Member] BARDA, Other Transaction Agreement Deferred revenue, noncurrent Contract with Customer, Liability, Noncurrent Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Classification of Investment [Domain] Classification of Investment [Domain] Provides general categories of investments for which information is required or determined to be disclosed. Praluent Praluent Net Product Sales [Member] Praluent Net Product Sales 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. Redemption price, percentage Debt Instrument, Redemption Price, Percentage Common Stock Common Stock Common Stock Common Stock [Member] Product and Service [Domain] Product and Service [Domain] Libtayo development Libtayo Development [Member] Libtayo Development [Member] Schedule of collaboration revenue Collaborative Arrangement and Arrangement Other than Collaborative [Table Text Block] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Sovereign bonds Sovereign bonds Sovereign Debt Securities [Member] Common Stock Held By Sanofi Common Stock Held By Sanofi [Member] Common Stock Held By Sanofi Number of IPR filed Gain Contingency, Inter Partes Review Filed, Number Gain Contingency, Inter Partes Review Filed, Number Class of Treasury Stock [Table] Class of Treasury Stock [Table] Bayer Bayer Collaboration Agreement [Member] Bayer Collaboration Agreement [Member] Restatement [Domain] Revision of Prior Period [Domain] Interest rate Debt Instrument, Interest Rate, Stated Percentage Unrealized Loss - Less than 12 months Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Class A Stock Common Class A [Member] Product and service, other Product and Service, Other [Member] Net decrease in cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Total other income (expense) Nonoperating Income (Expense) Error Corrections and Prior Period Adjustments Restatement [Line Items] Error Corrections and Prior Period Adjustments Restatement [Line Items] Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Stock options Share-based Payment Arrangement, Option [Member] Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Equity, Class of Treasury Stock [Line Items] Equity, Class of Treasury Stock [Line Items] Weighted average shares outstanding - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Expenses: Costs and Expenses [Abstract] Treasury Stock (in shares) Treasury Stock, Shares Reduction of Research and development expense Reduction of Research and development expense Reimbursement Of Research And Development Expense Reimbursement Of Research And Development Expense Dupilumab/REGN3500 Eligible Investments Dupilumab/REGN3500 Eligible Investments [Member] Dupilumab/REGN3500 Eligible Investments [Member] Loss Contingencies [Table] Loss Contingencies [Table] Securities owned not readily marketable Equity Securities without Readily Determinable Fair Value, Amount Interim Financial Statements Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Additional paid-in capital Additional Paid in Capital Long-term debt fair value Long-term Debt, Fair Value Class of Stock [Axis] Class of Stock [Axis] Income tax expense Income Tax Expense (Benefit) 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 Debt Securities, Available-for-sale [Table] Debt Securities, Available-for-sale [Table] Purchases of marketable and other securities Payments to Acquire Marketable Securities New Accounting Pronouncements or Change in Accounting Principle [Table] Accounting Standards Update and Change in Accounting Principle [Table] Net income per share - diluted (in dollars per share) Earnings Per Share, Diluted Cumulative Effect, Period of Adoption [Domain] Cumulative Effect, Period of Adoption [Domain] Accrued expenses and other current liabilities Accrued Liabilities and Other Liabilities Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] REGN-COV2 REGN-COV2 [Member] REGN-COV2 Deferred revenue Contract with Customer, Liability Project [Axis] Project [Axis] Award Type [Axis] Award Type [Axis] Maximum Maximum [Member] Security Exchange Name Security Exchange Name Preferred Stock, shares authorized (in shares) Preferred Stock, Shares Authorized Restricted cash included in Other noncurrent assets Restricted Cash Retained Earnings Retained Earnings [Member] Preferred Stock, shares outstanding (in shares) Preferred Stock, Shares Outstanding Measurement Basis [Axis] Measurement Basis [Axis] Short-term Debt, Type [Domain] Short-term Debt, Type [Domain] Effective income tax rate Effective Income Tax Rate Reconciliation, Percent 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] Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities Pending Litigation Pending Litigation [Member] Award Type [Domain] Award Type [Domain] Investments [Domain] Investments [Domain] Document Transition Report Document Transition Report 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] Realized gain (loss) on sales of marketable securities Marketable Securities, Realized Gain (Loss) Litigation Status [Domain] Litigation Status [Domain] Treasury Stock, at cost; 15,741,824 shares in 2020 and 4,860,123 shares in 2019 Treasury Stock, Value Net Income Per Share Earnings Per Share [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization, Consolidation and Presentation of Financial Statements [Abstract] Current liabilities: Liabilities, Current [Abstract] Measured on a recurring basis Fair Value, Recurring [Member] 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 Recently Adopted Accounting Standards New Accounting Pronouncements, Policy [Policy Text Block] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Redemption price with change-in-control provision, percentage Debt Instrument, Redemption Price With Change-In-Control Provision, Percentage Debt Instrument, Redemption Price With Change-In-Control Provision, Percentage