Strategic Alliances and Collaborations (Revenue from Strategic Alliances) (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenue from External Customer [Line Items]
Total revenues	$ 489	$ 4,200
Strategic Alliances and Collaborations
Revenue from External Customer [Line Items]
Total revenues	489	4,200
Strategic Alliances and Collaborations | AstraZeneca
Revenue from External Customer [Line Items]
Total revenues	471	3,582
Strategic Alliances and Collaborations | Sanofi
Revenue from External Customer [Line Items]
Total revenues	18	18
Strategic Alliances and Collaborations | Biogen
Revenue from External Customer [Line Items]
Total revenues	$ 0	$ 600