Collaboration Agreements Schedule of Collaboration Revenue Earned From Sanofi (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues	$ 1,608,022	$ 1,470,116	$ 3,119,507	$ 2,789,107
Product and service, other | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	131,005	133,299	219,279	264,987
Product and service, other | Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	106,748	88,829	207,964	167,508
Product and service, other | Sanofi
Disaggregation of Revenue [Line Items]
Revenues	237,753	222,128	427,243	432,495
Reimbursement of Regeneron research and development expenses | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	64,482	137,272	124,876	292,517
Reimbursement of Regeneron research and development expenses | Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	77,054	68,080	150,878	126,759
Reimbursement of Regeneron commercialization-related expenses | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	103,666	87,104	189,090	160,663
Reimbursement of Regeneron commercialization-related expenses | Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	2,061	749	3,271	749
Regeneron's share of losses in connection with commercialization of antibodies | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	(68,797)	(122,281)	(143,671)	(230,683)
Other | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Revenues	31,654	31,204	48,984	42,490
Other | Sanofi Collaboration Agreement, Immuno-oncology
Disaggregation of Revenue [Line Items]
Revenues	$ 27,633	$ 20,000	$ 53,815	$ 40,000