Comparison of Reported Condensed Consolidated Statement of Operations Under New Guidance (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenues:
Collaboration and license revenue	$ 4,011	$ 3,787	$ 10,655	$ 8,915
Operating expenses:
Research and development	66,440	49,292	126,507	79,937
Loss from operations	(103,695)	(65,834)	(188,995)	(106,372)
Net loss	(105,971)	(69,414)	(190,481)	(111,178)
Net loss attributable to Portola	$ (106,194)	$ (69,654)	$ (190,372)	$ (111,373)
Basic and diluted	$ (1.61)	$ (1.22)	$ (2.90)	$ (1.96)
Collaboration and License Revenue
Revenues:
Collaboration and license revenue	$ 1,746	$ 3,787	$ 7,784	$ 8,915
Balances Without the Adoption of ASC 606 | Accounting Standards Update 2014-09
Operating expenses:
Research and development	65,676		125,021
Loss from operations	(103,107)		(187,368)
Net loss	(105,383)		(188,854)
Net loss attributable to Portola	$ (105,606)		$ (188,745)
Basic and diluted	$ (1.60)		$ (2.87)
Balances Without the Adoption of ASC 606 | Collaboration and License Revenue | Accounting Standards Update 2014-09
Revenues:
Collaboration and license revenue	$ 1,569		$ 7,925
Effect of Change | Accounting Standards Update 2014-09
Operating expenses:
Research and development	764		1,486
Loss from operations	(588)		(1,627)
Net loss	(588)		(1,627)
Net loss attributable to Portola	$ (588)		$ (1,627)
Basic and diluted	$ (0.01)		$ (0.03)
Effect of Change | Collaboration and License Revenue | Accounting Standards Update 2014-09
Revenues:
Collaboration and license revenue	$ 177		$ (141)