Collaboration Agreements - Revenue Recognized from Collaborations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue	$ 264	$ 412	$ 294	$ 1,393
Teva [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue	14	29	44	87
Genentech [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue		$ 383		1,149
Genentech [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue				$ 157
Genentech [Member] | Milestone Payment [Member] | Collaborative Arrangement [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaboration revenue	$ 250		$ 250