Revenue from Strategic Alliances (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenue from External Customer [Line Items]
Total revenues	$ 1,083	$ 6,118	$ 3,450	$ 14,115
Strategic Alliances and Collaborations
Revenue from External Customer [Line Items]
Total revenues	1,083	6,118	3,450	14,115
Strategic Alliances and Collaborations | Sanofi
Revenue from External Customer [Line Items]
Total revenues	18	5,422	961	10,828
Strategic Alliances and Collaborations | Astra Zeneca
Revenue from External Customer [Line Items]
Total revenues	465	465	1,394	1,394
Strategic Alliances and Collaborations | GSK
Revenue from External Customer [Line Items]
Total revenues	144	144	433	1,634
Strategic Alliances and Collaborations | Biogen Idec
Revenue from External Customer [Line Items]
Total revenues	449	87	622	259
Strategic Alliances and Collaborations | Other
Revenue from External Customer [Line Items]
Total revenues	$ 7		$ 40