Collaborative Arrangements and Acquisitions - Merck KGaA (Details)		3 Months Ended			9 Months Ended
	Jan. 10, 2017 USD ($) pre-clinical_stage_program clinical-stage_program development_program	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenues		$ 26,292,000		$ 259,000	$ 286,123,000	$ 1,008,000
Merck KGaA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Right to license, number of development programs | development_program	4
Right to license, number of clinical stage programs | clinical-stage_program	2
Number of pre-clinical stage programs | pre-clinical_stage_program	2
Collaborative arrangement, up-front payment	$ 230,000,000.0
Proceeds from collaborators			$ 193,600,000
Collaborative revenues		$ 5,200,000			$ 12,800,000
Collaborative revenues, related to upfront payment upon delivery of license and to research and development transition activities			231,700,000
Time period of notice required to terminate	90 days
Time period of notice required to terminate after a product has received marketing approval	180 days
German Tax Authority | Merck KGaA
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative revenues, tax withholding			$ 36,400,000