Collaboration Agreements - Revenue Recognized from Collaborations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Collaboration Revenue [Line Items]
Collaboration revenue	$ 412	$ 4,044	$ 981	$ 8,054
Teva [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue		2,908		5,784
Teva [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue	29	45	58	90
Genentech [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue		181	157	360
Genentech [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue	$ 383	$ 910	$ 766	$ 1,820