Quarterly Financial Information (unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information [Line Items]
Total revenues									$ 40,130	$ 22,546	$ 35,504
Operating expenses	$ (102,479)	$ (83,321)	$ (107,706)	$ (91,944)	$ (95,654)	$ (84,284)	$ (69,621)	$ (45,666)	(385,450)	(295,225)	(305,089)
Net loss	(88,886)	(71,177)	(105,971)	(84,510)	(91,501)	(82,941)	(69,414)	(41,764)	(350,544)	(285,620)	(268,113)
Net loss (income) attributable to noncontrolling interest (SRX Cardio)	338	(126)	(223)	332	(280)	5	(240)	45	321	(470)	(930)
Net loss attributable to Portola	$ (88,548)	$ (71,303)	$ (106,194)	$ (84,178)	$ (91,781)	$ (82,936)	$ (69,654)	$ (41,719)	$ (350,223)	$ (286,090)	$ (269,043)
Net loss per share attributable to Portola common stockholders:
Basic and diluted	$ (1.34)	$ (1.08)	$ (1.61)	$ (1.28)	$ (1.41)	$ (1.41)	$ (1.22)	$ (0.74)	$ (5.31)	$ (4.81)	$ (4.76)
Product Revenue, Net
Quarterly Financial Information [Line Items]
Total revenues	$ 14,070	$ 7,176	$ 2,265	$ 606					$ 24,117
Collaboration and License Revenue
Quarterly Financial Information [Line Items]
Total revenues	$ 1,228	$ 7,001	$ 1,746	$ 6,038	$ 9,803	$ 3,828	$ 3,787	$ 5,128	$ 16,013	$ 22,546	$ 35,504