Weighted-Average Fair Value of Performance Stock Units (Parenthetical) (Detail) (Performance Shares, USD $)	3 Months Ended
Mar. 31, 2015
Performance Shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Minimum average market closing price to earn PSU	$ 50
Minimum average closing price to earn PSU	$ 60.00

Minimum average market closing price to earn performance stock unit.

No definition available.

Name:	ptla_MinimumAverageMarketClosingPriceToEarnPerformanceStockUnit
Namespace Prefix:	ptla_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration