Collaboration and License Agreements - Additional Information (Detail) - USD ($)	1 Months Ended						3 Months Ended			6 Months Ended	9 Months Ended		24 Months Ended
	Jul. 31, 2014	Apr. 30, 2014	Jan. 31, 2014	Feb. 28, 2013	Jan. 31, 2013	Nov. 30, 2012	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2014	Jun. 30, 2013	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2015
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue							$ 2,912,000	$ 2,427,000			$ 7,656,000	$ 7,213,000
Research and development							48,405,000	31,780,000			140,563,000	88,918,000
Daiichi Sankyo, Inc ("Daiichi")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaborative arrangement upfront payment to be received										$ 6,000,000
Upfront fee subject to refund										$ 3,000,000
Non-contingent consideration being recognized as revenue over estimated period of performance									$ 3,000,000
Contingent and non-contingent consideration to be recognized after resolution of contingency							264,000	662,000			782,000	2,300,000
Deferred revenue							263,000				263,000
Upfront fee	$ 15,000,000
Contingent payment receivable upon achievement	5,000,000
Milestone Payments of Development and Regulatory Event	$ 20,000,000
Collaboration and license revenue							1,154,000	1,523,000			3,424,000	3,133,000
Daiichi Sankyo, Inc ("Daiichi") | Collaborative Agreement to Study Safety and Efficacy of Andexanet Alfa
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue							10,600,000				10,600,000
Collaboration and license revenue							890,000	861,000			2,600,000	861,000
Daiichi Sankyo, Inc ("Daiichi") | Collaborative Agreement to Study Safety and Efficacy of Andexanet Alfa | Future Contingent Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue											0
Daiichi Sankyo, Inc ("Daiichi") | Scenario Forecast
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent consideration to be recognized after resolution of contingency													$ 3,000,000
Bayer Pharma AG
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fee				$ 2,500,000
Additional non-refundable fee				250,000
Janssen Pharmaceuticals, Inc.
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fee				2,500,000
Additional non-refundable fee				250,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fee			$ 10,000,000	5,000,000
Contingent payment receivable upon achievement			7,000,000
Milestone Payments of Development and Regulatory Event			8,000,000
Collaboration and license revenue							1,316,000	676,000			2,922,000	2,782,000
Additional non-refundable fee				$ 500,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | February 2013 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue							0				0
Collaboration and license revenue							500,000	316,000			500,000	1,100,000
Collaborative Arrangement Payment Received							500,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | January 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue							8,100,000				8,100,000
Collaboration and license revenue							816,000	361,000			2,400,000	1,700,000
Contingent Payments Received											3,000,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | Future Contingent Payments | January 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue											0
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-contingent consideration being recognized as revenue over estimated period of performance											6,500,000
Contingent consideration to be recognized after resolution of contingency											6,500,000
Upfront fee			13,000,000
Milestone Payments of Development and Regulatory Event			$ 12,000,000
Collaboration and license revenue							388,000	164,000			1,152,000	1,109,000
Percentage of consideration received under agreement			50.00%
Milestone payments of regulatory and clinical event											10,000,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | January 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue							10,300,000				10,300,000
Collaboration and license revenue							388,000	164,000			1,200,000	1,100,000
Lee’s Pharmaceutical (HK) Ltd (“Lee’s”)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue							104,000				104,000
Upfront fee					$ 700,000
Collaboration and license revenue							54,000	64,000			$ 158,000	189,000
Notice period for agreement termination					60 days
Ora, Inc. (“Ora”)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Notice period for agreement termination											90 days
Development costs, percent											60.00%
Percentage of profits entitle to receive under agreement											50.00%
Rights to buy compound interests and licensed agreements											Each party may also buy out the rights and interests in the licensed compound by paying the greater of $6.0 million or two times the actual aggregate development cost incurred by both parties before or 90 days after an End of Phase 2 meeting with the FDA.
Research and development							230,000				$ 230,000
Ora, Inc. (“Ora”) | PORTOLA PHARMACEUTICALS INC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs, percent											40.00%
Aciex Therapeutics, Inc. (“Aciex”)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs, percent											60.00%
Percentage of profits entitle to receive under agreement											50.00%
Research and development							0	0			$ 0	0
Aciex Therapeutics, Inc. (“Aciex”) | PORTOLA PHARMACEUTICALS INC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs, percent											40.00%
Biogen Idec
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License fee receivable upon occurrence of certain development and regulatory events						$ 370,000,000
Payments Upon the Completion of Certain Commercial Milestones		$ 15,000,000
Reduction in research and development expense							$ 0	$ 23,080			$ 0	$ 178,700