Collaboration and License Agreements - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended								12 Months Ended			1 Months Ended					12 Months Ended	1 Months Ended				6 Months Ended
	May 31, 2013	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	Apr. 30, 2012	Feb. 28, 2009	Apr. 30, 2014	Nov. 30, 2012	Oct. 31, 2011	Dec. 31, 2011	Jan. 31, 2014	Jan. 31, 2013	Feb. 28, 2013	Jul. 31, 2014	Jun. 30, 2013
Research And Development Arrangement Contract To Perform For Others [Line Items]
Increase in collaborative revenue										$ 31,374,000	$ 1,169,000	$ (65,426,000)
Net (loss) income		(39,256,000)	(35,793,000)	(31,350,000)	(30,726,000)	(25,062,000)	(18,550,000)	(21,598,000)	(18,142,000)	(137,125,000)	(83,352,000)	11,366,000
Net income (loss) per share		$ (0.82)	$ (0.86)	$ (0.76)	$ (0.75)	$ (0.63)	$ (0.53)	$ (1.47)	$ (12.94)
Sale of stock, value										174,621,000
Stock issued during the period	9,686,171
Research and development										123,639,000	79,286,000	49,717,000
PORTOLA PHARMACEUTICALS INC
Research And Development Arrangement Contract To Perform For Others [Line Items]
Development costs, percent										40.00%
Novartis AG ("Novartis")
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront fee														75,000,000
License fee receivable upon occurrence of certain development and regulatory events														505,000,000
Clinical trial costs company must fund														18,000,000
Increase in collaborative revenue													65,100,000
Net income (loss) per share													$ 0.00
Novartis AG ("Novartis") | Absent Collaboration Revenue Acceleration
Research And Development Arrangement Contract To Perform For Others [Line Items]
Impact of scenario on net income													(65,100,000)
Net (loss) income													53,700,000
Net income (loss) per share													$ (3.98)
Biogen Idec
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront fee																	36,000,000
License fee receivable upon occurrence of certain development and regulatory events																370,000,000
Estimated partial reimbursement of research and development services																	22,900,000
Performance period																	2 years
Reduction in research and development expense										210,000	804,000	6,500,000						734,000
Notice period for agreement termination																120 days
Payments Upon the Completion of Certain Commercial Milestones															15,000,000
Biogen Idec | Convertible Preferred Stock
Research And Development Arrangement Contract To Perform For Others [Line Items]
Sale of stock, value																	9,000,000
Stock issued during the period																	636,042
Premium on sale of stock																	1,100,000
Biogen Idec | Collaborative Arrangement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized																		37,100,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer")
Research And Development Arrangement Contract To Perform For Others [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
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | October 2012 Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue						6,000,000					6,000,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | January 2014 Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized										1,500,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Collaborative Arrangement | October 2012 Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized											4,000,000	2,000,000
Bristol-Myers Squibb Company ("BMS") and Pfizer Inc. ("Pfizer") | Collaborative Arrangement | January 2014 Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue		11,500,000								11,500,000
Lee’s Pharmaceutical (HK) Ltd (“Lee’s”)
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront fee																				700,000
Notice period for agreement termination																				60 days
Deferred revenue		263,000								263,000
Lee’s Pharmaceutical (HK) Ltd (“Lee’s”) | Collaborative Arrangement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized										243,000	194,000
Bayer Pharma AG
Research And Development Arrangement Contract To Perform For Others [Line Items]
Additional non-refundable fee																					250,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen")
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront fee																			10,000,000
Milestone Payments of Development and Regulatory Event																			8,000,000
Additional non-refundable fee																					500,000
Contingent payment receivable upon achievement																			7,000,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | January 2014 Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue		10,500,000								10,500,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | February 2013 Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue		0								0
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | Collaborative Arrangement | January 2014 Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized										2,500,000
Contingent Payments Received										3,000,000
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | Collaborative Arrangement | January 2014 Agreement | Future Contingent Payments
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized										0
Bayer Pharma, AG ('Bayer") and Janssen Pharmaceuticals, Inc. ("Janssen") | Collaborative Arrangement | February 2013 Agreement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized										1,100,000	3,900,000
Janssen Pharmaceuticals, Inc.
Research And Development Arrangement Contract To Perform For Others [Line Items]
Additional non-refundable fee																					250,000
Aciex Therapeutics, Inc. (“Aciex”)
Research And Development Arrangement Contract To Perform For Others [Line Items]
Development costs, percent										60.00%
Research and development										0	0
Daiichi Sankyo, Inc ("Daiichi")
Research And Development Arrangement Contract To Perform For Others [Line Items]
Upfront fee																						15,000,000
Milestone Payments of Development and Regulatory Event																						20,000,000
Non-contingent consideration being recognized as revenue over estimated period of performance										3,000,000
Contingent consideration to be recognized after resolution of contingency										3,000,000
Contingent payment receivable upon achievement																						5,000,000
Collaborative arrangement upfront payment to be received																							6,000,000
Upfront fee subject to refund																							3,000,000
Daiichi Sankyo, Inc ("Daiichi") | Collaborative Agreement to Study Safety and Efficacy of Andexanet Alfa
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue		13,200,000								13,200,000
Daiichi Sankyo, Inc ("Daiichi") | Collaborative Agreement to Study Safety and Efficacy of Andexanet Alfa | Future Contingent Payments
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized										0
Daiichi Sankyo, Inc ("Daiichi") | Collaborative Arrangement
Research And Development Arrangement Contract To Perform For Others [Line Items]
Deferred revenue		1,000,000								1,000,000
Contingent consideration to be recognized after resolution of contingency										2,500,000
Daiichi Sankyo, Inc ("Daiichi") | Collaborative Arrangement | Collaborative Agreement to Study Safety and Efficacy of Andexanet Alfa
Research And Development Arrangement Contract To Perform For Others [Line Items]
Collaboration revenue recognized										$ 1,800,000