Stock-Based Compensation - Additional Information (Detail) - $ / shares	3 Months Ended	6 Months Ended
	Mar. 31, 2015	Jun. 30, 2015
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Percentage increase in number of common stock outstanding		5.00%
Number of common stock shares reserved for issuance under the 2013 Equity Incentive Plan		9,445,589
Restricted Stock Units (RSUs)
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Vesting period	3 years
Shares awarded to certain employees on achievement of certain performance goals (performance based RSUs)		182,825
Performance Shares
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Vesting period		4 years
Number of common stock earned per share		1
Consecutive trading period required to earn PSU		45 days
Vesting rights		At any time during the four years following the date of the grant, a portion of the PSUs will vest one year after the date the average closing price of Portola’s stock on the NASDAQ Global Select Market is above $50.00 per share for 45 consecutive trading days, and the remaining portion of the grant will vest one year after the date the average closing price of Portola’s stock is above $60.00 per share for 45 consecutive trading days
Shares awarded to certain employees on achievement of certain performance goals (performance based RSUs)		165,000
Performance Shares | Maximum
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Shares awarded to certain employees on achievement of certain performance goals (performance based RSUs)		69,625
Performance Shares | $50 Vesting Hurdle
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Minimum average market closing price to earn PSU		$ 50.00
Performance Shares | $60 Vesting Hurdle
Deferred Compensation Arrangement With Individual Share Based Payments [Line Items]
Minimum average market closing price to earn PSU		$ 60.00