Summary of Revenue from Collaboration and License Agreements (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue	$ 2,411	$ 2,427	$ 2,415	$ 2,372	$ 2,056	$ 2,766	$ 2,601	$ 3,108	$ 9,625	$ 10,531	$ 72,042
Novartis AG ("Novartis")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue											70,084
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									1,497	4,042	1,958
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen"), Collaborative arrangements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									3,598	3,876
Lee’s Pharmaceutical (HK) Ltd (“Lee’s”)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									243	194
Daiichi Sankyo, Inc ("Daiichi"), Collaborative arrangements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									4,287	2,419
Licensing Agreements | Novartis AG ("Novartis")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue											53,846
Reimbursement of research and development expense											16,238
Licensing Agreements | Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									1,497	4,042	1,958
Licensing Agreements | Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen"), Collaborative arrangements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									3,598	3,876
Licensing Agreements | Lee’s Pharmaceutical (HK) Ltd (“Lee’s”)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									243	194
Licensing Agreements | Daiichi Sankyo, Inc ("Daiichi"), Collaborative arrangements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									$ 4,287	$ 2,419