Collaboration and License Agreements - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended		9 Months Ended			3 Months Ended	9 Months Ended	1 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	1 Months Ended			3 Months Ended	9 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Nov. 30, 2012 Biogen Idec	Sep. 30, 2013 Biogen Idec	Sep. 30, 2012 Biogen Idec	Sep. 30, 2013 Biogen Idec	Sep. 30, 2012 Biogen Idec	Oct. 31, 2013 Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")	Sep. 30, 2013 Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") Collaborative Arrangement	Sep. 30, 2013 Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") Collaborative Arrangement	Jan. 31, 2013 Lee's Pharmaceutical (HK) Ltd ("Lee's")	Sep. 30, 2013 Lee's Pharmaceutical (HK) Ltd ("Lee's") Collaborative Arrangement	Sep. 30, 2013 Lee's Pharmaceutical (HK) Ltd ("Lee's") Collaborative Arrangement	Sep. 30, 2013 Aciex Therapeutics, Inc. (Aciex)	Sep. 30, 2013 Aciex Therapeutics, Inc. (Aciex)	Feb. 01, 2013 Bayer Pharma AG	Feb. 01, 2013 Janssen Pharmaceuticals, Inc.	Feb. 01, 2013 Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen")	Sep. 30, 2013 Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") Collaborative Arrangement	Sep. 30, 2013 Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") Collaborative Arrangement	Jun. 30, 2013 Daiichi Sankyo, Inc ("Daiichi")	Sep. 30, 2013 Daiichi Sankyo, Inc ("Daiichi")	Sep. 30, 2013 Daiichi Sankyo, Inc ("Daiichi") Collaborative Arrangement	Sep. 30, 2013 Daiichi Sankyo, Inc ("Daiichi") Collaborative Arrangement	Sep. 30, 2013 PORTOLA PHARMACEUTICALS INC
Research And Development Arrangement Contract To Perform For Others [Line Items]
License fee receivable upon occurrence of certain development and regulatory events					$ 370,000,000
Notice period for agreement termination					120 days								60 days
Reduction in research and development expense						227,000	1,000,000	721,000	5,900,000
Deferred revenue										6,000,000	176,000	176,000		570,000	570,000						1,500,000	1,500,000
Collaboration revenue recognized											772,000	3,900,000		78,000	130,000						1,000,000	3,500,000			888,000	1,000,000
Upfront and non-refundable fee													700,000					2,500,000	2,500,000	5,000,000
Development costs, percent																	60.00%										40.00%
Research and development	18,088,000	9,954,000	56,642,000	36,004,000												0	0
Additional non-refundable fee																		250,000	250,000	500,000
Collaborative arrangement up front payment to be received																							6,000,000
Upfront fee subject to refund																							3,000,000
Contingent consideration of collaboration arrangement																									3,000,000	3,000,000
Non-contingent consideration being recognized as revenue over estimated period of performance																								3,000,000		2,000,000
Contingent consideration to be recognized after resolution of contingency																								$ 3,000,000