Collaboration Agreements - Revenue Recognized from Collaborations (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Collaboration Revenue [Line Items]
Collaboration revenue	$ 569	$ 4,010
Teva [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue		2,876
Teva [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue	29	45
Genentech [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue	157	179
Genentech [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue	$ 383	$ 910