Strategic Alliances and Collaborations - Revenue from Strategic Alliances (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue from External Customer [Line Items]
Total revenues	$ 10,860	$ 1,865	$ 3,834	$ 4,200	$ 4,219	$ 1,083	$ 736	$ 1,631	$ 20,759	$ 7,669	$ 19,569
Strategic Alliances and Collaborations
Revenue from External Customer [Line Items]
Total revenues									20,759	7,669	19,569
Strategic Alliances and Collaborations | AstraZeneca
Revenue from External Customer [Line Items]
Total revenues									18,871	1,859	1,859
Strategic Alliances and Collaborations | Sanofi
Revenue from External Customer [Line Items]
Total revenues									71	979	15,336
Strategic Alliances and Collaborations | GSK
Revenue from External Customer [Line Items]
Total revenues									0	3,509	1,778
Strategic Alliances and Collaborations | Biogen
Revenue from External Customer [Line Items]
Total revenues									1,817	1,122	596
Strategic Alliances and Collaborations | Other
Revenue from External Customer [Line Items]
Total revenues									$ 0	$ 200	$ 0