Collaboration Agreements - Revenue Recognized from Collaborations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Collaboration Revenue [Line Items]
Collaboration revenue	$ 412	$ 4,293	$ 1,393	$ 12,347
Teva [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue		2,940		8,724
Teva [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue	29	11	87	101
Genentech [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue		182	157	542
Genentech [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue	$ 383	910	$ 1,149	2,730
Genentech [Member] | Milestone Payment [Member] | Collaborative Arrangement [Member]
Collaboration Revenue [Line Items]
Collaboration revenue		$ 250		$ 250