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Deposit [Member] Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested Year-over-Year Change in Fair Value of Equity Awards Granted in Prior Years That are Outstanding and Unvested [Member] 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 Cash flows from financing activities: Net Cash Provided by (Used in) Financing Activities [Abstract] Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested Year-end Fair Value of Equity Awards Granted in Covered Year that are Outstanding and Unvested [Member] Concentration Risk [Line Items] Concentration Risk [Line Items] Preferred Stock, par value $.01 per share; 30.0 shares authorized; shares issued and outstanding - none Preferred Stock, Value, Issued Net income per share - basic (in dollars per share) Earnings Per Share, Basic Proceeds from issuance of Common Stock Proceeds from Issuance of Common Stock Adjustment To PEO Compensation, Footnote Adjustment To PEO Compensation, Footnote [Text Block] Award Timing MNPI Disclosure Award Timing MNPI Disclosure [Text Block] Property, plant, and equipment, net Property, Plant, and Equipment and Finance Lease Right-of-Use Asset, after Accumulated Depreciation and Amortization Accrued capital expenditures Capital Expenditures Incurred but Not yet Paid Aggregate Pension Adjustments Service Cost Aggregate Pension Adjustments Service Cost [Member] Bayer Bayer Collaboration Agreement [Member] Bayer Collaboration Agreement [Member] Compensation Actually Paid vs. Other Measure Compensation Actually Paid vs. Other Measure [Text Block] Fair Value and Unrealized Losses of Marketable Securities Debt Securities, Available-for-Sale, Unrealized Loss Position, Fair Value [Table Text Block] Schedule of Stock by Class [Table] Stock, Class of Stock [Table] Total current liabilities Liabilities, Current Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year Vesting Date Fair Value of Equity Awards Granted and Vested in Covered Year [Member] Share Repurchase Program [Axis] Share Repurchase Program [Axis] Total assets Assets Cost of goods, collaboration and contract manufacturing Cost of Goods and Services Sold 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] Cash and Cash Equivalents [Abstract] Other noncurrent liabilities Other Liabilities, Noncurrent Forgone Recovery due to Violation of Home Country Law, Amount Forgone Recovery due to Violation of Home Country Law, Amount Termination Date Trading Arrangement Termination Date 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] Entity Address, City or Town Entity Address, City or Town 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 Net income Net income Net income - basic and diluted Net Income (Loss) Attributable to Parent Other operating expense (income), net Other Operating Income (Expense), Net Trading Arrangement: Trading Arrangement [Axis] Investments, Debt and Equity Securities [Abstract] Investments, Debt and Equity Securities [Abstract] Pay vs Performance Disclosure, Table Pay vs Performance [Table Text Block] Loss Contingencies [Table] Loss Contingencies [Table] Equity Awards Adjustments, Excluding Value Reported in Compensation Table Equity Awards Adjustments, Excluding Value Reported in the Compensation Table [Member] Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year Dividends or Other Earnings Paid on Equity Awards not Otherwise Reflected in Total Compensation for Covered Year [Member] Entity File Number Entity File Number Liabilities, Fair Value Disclosure [Abstract] Liabilities, Fair Value Disclosure [Abstract] Product Sales Revenue from Contract with Customer [Text Block] Document Fiscal Year Focus Document Fiscal Year Focus Statements of Operations Income Statement [Abstract] Entity Address, Address Line One Entity Address, Address Line One Total cost of shares Treasury Stock, Value, Acquired, Cost Method Effect of exchange rate changes on cash, cash equivalents, and restricted cash Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Continuing Operations Total assets Assets, Fair Value Disclosure Name Forgone Recovery, Individual Name Document Period End Date Document Period End Date Loss Contingency, Nature [Domain] Loss Contingency, Nature [Domain] Deferred income taxes Increase (Decrease) in Deferred Income Taxes Finished goods Inventory, Finished Goods, Net of Reserves Other non-cash items, net Other Noncash Income (Expense) Award Timing MNPI Considered Award Timing MNPI Considered [Flag] Insider Trading Arrangements [Line Items] Inventory Disclosure [Abstract] Inventory Disclosure [Abstract] Outstanding Aggregate Erroneous Compensation Amount Outstanding Aggregate Erroneous Compensation Amount PEO Actually Paid Compensation Amount PEO Actually Paid Compensation Amount Adjustment to Compensation: Adjustment to Compensation [Axis] Prepaid expenses and other current assets Prepaid Expense and Other Assets, Current Document Transition Report Document Transition Report Document Quarterly Report Document Quarterly Report Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Customer [Domain] Customer [Domain] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Current Reporting Status Entity Current Reporting Status Retained Earnings Retained Earnings [Member] Pension Adjustments Service Cost Pension Adjustments Service Cost [Member] Weighted average shares outstanding - basic (in shares) Weighted average shares - basic (in shares) Weighted Average Number of Shares Outstanding, Basic Stock Price or TSR Estimation Method Stock Price or TSR Estimation Method [Text Block] 12 Months or Greater Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Document Information [Table] Document Information [Table] Acquired in-process research and development Acquired In-Process Research and Development Acquired In-Process Research and Development Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Executive Category: Executive Category [Axis] Name Awards Close in Time to MNPI Disclosures, Individual Name Less than 12 Months Debt Securities, Available-for-Sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss Entity Filer Category Entity Filer Category Regeneron's obligation for its share of Sanofi R&D expenses, net of reimbursement of R&D expenses Reimbursement Of Research And Development Expenses, Net Of Obligation For Share Of R&D Expenses [Member] Reimbursement Of Research And Development Expenses, Net Of Obligation For Share Of R&D Expenses Income Statement Location [Domain] Statement of Income Location, Balance [Domain] Loss Contingencies [Line Items] Loss Contingencies [Line Items] Company Selected Measure Name Company Selected Measure Name