License and Collaboration Agreements - Schedule of Revenue Recognized and Assets and Liabilities under Collaborative Arrangements (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total	$ 17,090,000	$ 16,440,000	$ 36,558,000	$ 14,842,000	$ 33,905,000	$ 28,002,000	$ 27,815,000	$ 13,034,000	$ 84,930,000	$ 102,756,000	$ 47,786,000
Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total									0
License and Collaboration Agreements [Member] | Baxalta [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Proportional performance revenue recognition model									64,930,000	10,460,000
Substantive milestones									20,000,000
Total									84,930,000	10,460,000
Accounts receivable, billed	1,336,000								1,336,000
Accounts receivable, unbilled	626,000				1,615,000				626,000	1,615,000
Deferred revenue	$ 97,365,000				91,156,000				$ 97,365,000	91,156,000
License and Collaboration Agreements [Member] | Sanofi [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment										39,306,000	5,000,000
Milestone payment										16,377,000	2,083,000
Development services										18,904,000	36,283,000
Manufacturing services and other										17,709,000	3,867,000
Total										92,296,000	$ 47,233,000
Accounts receivable, billed					369,000					369,000
Accounts receivable, unbilled					$ 1,282,000					$ 1,282,000