Collaboration Agreements - Financial Terms (Details) - Celgene - 2016 Agreement	1 Months Ended	3 Months Ended
	May 31, 2016 USD ($) special_case_extension	Mar. 31, 2017 USD ($)	May 17, 2016 USD ($) special_case_extension
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Initial payment received	$ 200,000,000	$ 8,000,000
Extension period	2 years
Number of allowable special case extensions | special_case_extension	4		4
Upfront payment agreement extension fee receivable	$ 40,000,000
Option exercise fee receivable			$ 30,000,000
Additional option exercise fee for further development			10,000,000
Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Minimum option exercise fee receivable for continuation program			$ 35,000,000