Collaboration and License Agreements - Additional Information (Detail) - USD ($)	1 Months Ended							3 Months Ended										12 Months Ended
	Oct. 31, 2016	Mar. 31, 2016	Feb. 29, 2016	Jul. 31, 2014	Jan. 31, 2014	Jun. 30, 2013	Feb. 28, 2013	Sep. 30, 2018	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Sep. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue									$ 13,693,000	$ 9,322,000	$ 4,231,000	$ 8,258,000	$ 4,414,000	$ 2,912,000	$ 2,385,000	$ 2,359,000		$ 35,504,000	$ 12,070,000	$ 9,625,000
Research and development																		246,854,000	200,376,000	123,639,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fee					$ 13,000,000
Milestone payments of development and regulatory event					$ 12,000,000
Percentage of consideration received under agreement					50.00%
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
Milestone payments of regulatory and clinical event																		3,500,000
Collaboration and license revenue																		6,583,000	1,540,000	1,497,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | January 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		2,200,000	1,500,000	1,500,000
Deferred revenue									11,200,000				8,400,000					11,200,000	8,400,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | February 2016 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		4,400,000
Deferred revenue									10,600,000									10,600,000
Non-refundable upfront fee			$ 15,000,000
Contingent payment receivable upon achievement of regulatory events			20,000,000
Contingent payment receivable upon achievement of annual net sales volumes			70,000,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | February 2016 Agreement | Future Contingent Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		$ 0
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | February 2016 Agreement | Minimum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalties entitle to receive under agreement																		5.00%
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | February 2016 Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of royalties entitle to receive under agreement																		15.00%
Daiichi Sankyo, Inc ("Daiichi")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fee				$ 15,000,000		$ 6,000,000
Milestone payments of development and regulatory event				20,000,000
Collaboration and license revenue																		$ 10,421,000	4,578,000	4,287,000
Deferred revenue									0				0					0	0
Contingent and non-contingent consideration to be recognized after resolution of contingency																			1,000,000	2,500,000
Contingent payment receivable upon achievement				$ 5,000,000
Daiichi Sankyo, Inc ("Daiichi") | Collaborative Agreement to Study Safety and Efficacy of Andexanet Alfa
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		9,200,000	3,500,000	1,800,000
Deferred revenue									12,600,000				9,700,000					12,600,000	9,700,000
Daiichi Sankyo, Inc ("Daiichi") | Future Contingent Payments | Collaborative Agreement to Study Safety and Efficacy of Andexanet Alfa
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		5,000,000
Daiichi Sankyo, Inc ("Daiichi") | October 2016 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fee	$ 15,000,000
Milestone payments of development and regulatory event	$ 2,500,000
Percentage of consideration received under agreement	1.00%
Contingent payment receivable upon achievement of annual net sales volumes	$ 8,000,000
Contingent payment receivable upon achievement	$ 10,000,000
Daiichi Sankyo, Inc ("Daiichi") | July 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contingent and non-contingent consideration to be recognized after resolution of contingency																		8,000,000
Daiichi Sankyo, Inc ("Daiichi") | July 2014 Agreement | Scenario Forecast
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-contingent consideration being recognized as revenue over estimated period of performance								$ 7,000,000
Daiichi Sankyo, Inc ("Daiichi") | March 2016 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		1,300,000
Deferred revenue									3,700,000									3,700,000
Daiichi Sankyo, Inc ("Daiichi") | March 2016 Agreement | ESS-Study
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement of costs and expenses percentage		33.00%
Daiichi Sankyo, Inc ("Daiichi") | March 2016 Agreement | Future Contingent Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		0
Daiichi Sankyo, Inc ("Daiichi") | March 2016 Agreement | Minimum | Edoxaban
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement of costs and expenses percentage		33.00%
Daiichi Sankyo, Inc ("Daiichi") | March 2016 Agreement | Maximum | Edoxaban
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement of costs and expenses percentage		100.00%
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen")
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fee		$ 5,000,000			$ 10,000,000		$ 5,000,000
Milestone payments of development and regulatory event					8,000,000
Collaboration and license revenue																		8,248,000	5,740,000	3,598,000
Contingent payment receivable upon achievement		10,000,000			$ 7,000,000
Reduced contingent payment receivable upon achievement		$ 7,000,000
Additional non-refundable fee							$ 500,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | January 2014 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		8,200,000	5,200,000
Deferred revenue									4,000,000				7,200,000					4,000,000	7,200,000
Contingent payment receivable upon achievement																	$ 3,000,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | January 2014 Agreement | Future Contingent Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		5,000,000		0
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | February 2013 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																			500,000	$ 1,100,000
Deferred revenue									0				$ 0					0	0
Bayer
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront fee			5,000,000
Collaboration and license revenue																		1,450,000
Contingent payment receivable upon achievement			10,000,000
Reduced contingent payment receivable upon achievement			$ 7,000,000
Bayer | February 2016 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		1,500,000
Deferred revenue									$ 3,500,000									3,500,000
Bayer | February 2016 Agreement | ESS-Study
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement of costs and expenses percentage			33.00%
Bayer | February 2016 Agreement | Future Contingent Payments
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		0
Bayer | February 2016 Agreement | Minimum | Rivaroxaban
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement of costs and expenses percentage			33.00%
Bayer | February 2016 Agreement | Maximum | Rivaroxaban
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement of costs and expenses percentage			100.00%
Dermavant Sciences GmbH (“Dermavant”)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Collaboration and license revenue																		$ 8,750,000
Percentage of royalties entitle to receive under agreement																		9.00%
Upfront payment received																		$ 8,800,000
Contingent development and regulatory milestones to be received																		36,300,000
Dermavant Sciences GmbH (“Dermavant”) | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Commercial milestone payments on worldwide annual net sales to be received																		$ 100,000,000
Ora, Inc. (“Ora”)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs, percent																		60.00%
Percentage of profits entitle to receive under agreement																		50.00%
Notice period for agreement termination																		90 days
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																		$ 629,000	$ 206,000
Ora, Inc. (“Ora”) | PORTOLA PHARMACEUTICALS INC
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development costs, percent																		40.00%