Strategic Alliances and Collaborations - Revenue from Strategic Alliances (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer [Line Items]
Total revenues	$ 18	$ 204	$ 483	$ 489	$ 10,860	$ 1,865	$ 3,834	$ 4,200	$ 1,194	$ 20,759	$ 7,669
Strategic Alliances and Collaborations
Revenue from External Customer [Line Items]
Total revenues									1,194	20,759	7,669
Strategic Alliances and Collaborations | AstraZeneca
Revenue from External Customer [Line Items]
Total revenues									1,122	18,871	1,859
Strategic Alliances and Collaborations | Sanofi
Revenue from External Customer [Line Items]
Total revenues									72	71	979
Strategic Alliances and Collaborations | GSK
Revenue from External Customer [Line Items]
Total revenues									0	0	3,509
Strategic Alliances and Collaborations | Biogen
Revenue from External Customer [Line Items]
Total revenues									0	1,817	1,122
Strategic Alliances and Collaborations | Other
Revenue from External Customer [Line Items]
Total revenues									$ 0	$ 0	$ 200