Collaboration Agreements Sanofi - Antibodies Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Research and development	$ 529,289	$ 509,975	$ 1,027,875	$ 1,017,410
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Annual funding maximum of research activities per amended agreement					$ 130,000
Percentage of Trial Costs borne by collaborating party			80.00%
Percentage of Trial Costs borne by entity			20.00%
Maximum amount of sales milestone payments if total sales achieve specific levels			$ 250,000
Levels of twelve month sales at which sales milestone payments would be received			$ 1,000,000
Period for achieving sales target for milestone payment, rolling basis			12 months
Praluent, Kevzara, and Dupixent | Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Research and development	$ 9,900	$ 20,600	$ 23,800	$ 45,600