Collaborative Arrangements - Janssen Pharmaceuticals, Inc. (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenues	$ 29,061	$ 26,292	$ 27,286	$ 232,545	$ 937	$ 259	$ 675	$ 74	$ 315,184	$ 1,945	$ 8,053
Janssen
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative arrangement, up-front payment												$ 35,000
Collaborative revenues	$ 25,000
Reimbursement for research and development activities									$ 2,000	$ 14,700	$ 22,800
Time period of notice required to terminate									6 months