Strategic Alliances and Collaborations (Revenue from Strategic Alliances) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Revenue from External Customer [Line Items]
Total revenues	$ 483	$ 3,834	$ 972	$ 8,034
Strategic Alliances and Collaborations
Revenue from External Customer [Line Items]
Total revenues	483	3,834	972	8,034
Strategic Alliances and Collaborations | AstraZeneca
Revenue from External Customer [Line Items]
Total revenues	465	3,066	936	6,648
Strategic Alliances and Collaborations | Sanofi
Revenue from External Customer [Line Items]
Total revenues	18	18	36	36
Strategic Alliances and Collaborations | Biogen
Revenue from External Customer [Line Items]
Total revenues	$ 0	$ 750	$ 0	$ 1,350