Summary of Revenue from Collaboration and License Agreements (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 2,359,000	$ 2,372,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	380,000	442,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	799,000	913,000
Lee’s Pharmaceutical (HK) Ltd (“Lee’s”)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	52,000	62,000
Daiichi Sankyo, Inc ("Daiichi")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 1,128,000	$ 955,000