Collaboration Agreements - Schedule of Collaboration Revenue Earned From Sanofi (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 1,663,496	$ 1,500,673	$ 4,783,003	$ 4,289,780
Product and service, other | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	174,058	162,411	393,337	427,398
Product and service, other | Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	82,207	82,764	290,171	250,272
Product and service, other | Sanofi
Disaggregation of Revenue [Line Items]
Revenues	256,265	245,175	683,508	677,670
Reimbursement of Regeneron research and development expenses | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	76,150	128,539	201,026	421,056
Reimbursement of Regeneron research and development expenses | Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	74,797	61,649	225,675	188,408
Reimbursement of Regeneron commercialization-related expenses | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	103,666	90,339	292,756	251,002
Reimbursement of Regeneron commercialization-related expenses | Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	3,236	1,115	6,507	1,864
Regeneron's share of losses in connection with commercialization of antibodies | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	(38,924)	(98,315)	(182,595)	(328,998)
Other | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	33,166	41,848	82,150	84,338
Other | Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	$ 4,174	$ 20,000	$ 57,989	$ 60,000