Collaboration Agreements - Revenue Recognized from Collaborations (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Deferred Revenue Arrangement [Line Items]
Collaboration revenue	$ 4,010	$ 5,001
Teva [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Deferred Revenue Arrangement [Line Items]
Collaboration revenue	2,876	3,025
Teva [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Deferred Revenue Arrangement [Line Items]
Collaboration revenue	45	80
Genentech [Member] | Recognition of Upfront Payment [Member] | Collaborative Arrangement [Member]
Deferred Revenue Arrangement [Line Items]
Collaboration revenue	179	786
Genentech [Member] | Research Funding [Member] | Collaborative Arrangement [Member]
Deferred Revenue Arrangement [Line Items]
Collaboration revenue	$ 910	$ 1,110