Agreements - Sanofi (Details) $ in Thousands		3 Months Ended		6 Months Ended
	May 30, 2017 USD ($) item	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($)
Collaborative Agreements disclosures
Milestone payment recorded in license and milestone fee revenue		$ 1,321	$ 31,080	$ 12,861	$ 49,810
Sanofi
Collaborative Agreements disclosures
Milestone payment recorded in license and milestone fee revenue					6,000
Sanofi | License amendments
Collaborative Agreements disclosures
Number of compounds | item	4
Payments received under collaboration agreement	$ 30,000
Sanofi | ASU 2014-09 | Previous guidance of ASC 605 | License amendments
Collaborative Agreements disclosures
Milestone payment recorded in license and milestone fee revenue			$ 30,000		$ 30,000