Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (68,477)	$ (105,971)	$ (146,573)	$ (190,481)
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net of tax	83	127	244	(265)
Foreign currency translation adjustment	(42)		(42)
Comprehensive loss	(68,436)	(105,844)	(146,371)	(190,746)
Comprehensive (income) loss attributable to noncontrolling interest	2,273	(223)	2,213	109
Total comprehensive loss attributable to Portola	$ (66,163)	$ (106,067)	$ (144,158)	$ (190,637)