Quarterly Financial Information (unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Collaboration and license revenue	$ 13,693	$ 9,322	$ 4,231	$ 8,258	$ 4,414	$ 2,912	$ 2,385	$ 2,359	$ 35,504	$ 12,070	$ 9,625
Operating expenses	(68,893)	(100,765)	(61,867)	(73,564)	(70,694)	(58,476)	(61,212)	(48,863)	(305,089)	(239,245)	(147,191)
Net loss	(54,764)	(91,036)	(57,339)	(64,974)	(66,105)	(55,158)	(58,329)	(46,913)	(268,113)	(226,505)	(137,125)
Net income attributable to noncontrolling interest (SRX Cardio)	923	(1,853)							(930)
Net loss attributable to Portola	$ (53,841)	$ (92,889)	$ (57,339)	$ (64,974)	$ (66,105)	$ (55,158)	$ (58,329)	$ (46,913)	$ (269,043)	$ (226,505)	$ (137,125)
Net loss per share attributable to Portola common stockholders:
Basic and diluted	$ (0.95)	$ (1.64)	$ (1.02)	$ (1.15)	$ (1.23)	$ (1.05)	$ (1.12)	$ (0.95)	$ (4.76)	$ (4.36)	$ (3.19)