Quarterly Financial Data (unaudited) - (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information [Line Items]
Total revenues									$ 116,640	$ 40,130	$ 22,546
Operating expenses	$ (119,391)	$ (80,381)	$ (92,384)	$ (95,768)	$ (102,479)	$ (83,321)	$ (107,706)	$ (91,944)	(387,924)	(385,450)	(295,225)
Net loss	(96,676)	(49,627)	(68,477)	(78,096)	(88,886)	(71,177)	(105,971)	(84,510)	(292,876)	(350,544)	(285,620)
Net loss (income) attributable to noncontrolling interest (SRX Cardio)	0	0	2,273	(60)	338	(126)	(223)	332	2,213	321	(470)
Net loss attributable to Portola	$ (96,676)	$ (49,627)	$ (66,204)	$ (78,156)	$ (88,548)	$ (71,303)	$ (106,194)	$ (84,178)	$ (290,663)	$ (350,223)	$ (286,090)
Net loss per share attributable to Portola common stockholders:
Basic and diluted (in dollars per share)	$ (1.24)	$ (0.68)	$ (0.97)	$ (1.17)	$ (1.34)	$ (1.08)	$ (1.61)	$ (1.28)	$ (4.06)	$ (5.31)	$ (4.81)
Product revenue, net
Quarterly Financial Information [Line Items]
Total revenues	$ 28,375	$ 35,743	$ 27,164	$ 20,362	$ 14,070	$ 7,176	$ 2,265	$ 606	$ 111,644	$ 24,117	$ 0
Collaboration and license revenue
Quarterly Financial Information [Line Items]
Total revenues	$ 873	$ 1,056	$ 1,260	$ 1,807	$ 1,228	$ 7,001	$ 1,746	$ 6,038	$ 4,996	$ 16,013	$ 22,546