Agreements - Sanofi (Details) $ in Thousands		3 Months Ended
	May 30, 2017 USD ($) item	Mar. 31, 2018 USD ($)	Mar. 31, 2017 USD ($)
Collaborative Agreements disclosures
License and milestone fees		$ 11,540	$ 18,730
Sanofi
Collaborative Agreements disclosures
Number of compounds | item	4
Payments received under collaboration agreement	$ 30,000
Sanofi | ASU 2014-09 | Adjustments due to new guidance
Collaborative Agreements disclosures
License and milestone fees			$ 6,000