Convertible Preferred Stock Warrant Liability - Additional Information (Detail)	Dec. 31, 2012
Convertible Preferred Stock Warrants [Line Items]
Warrant conversion rate	1

Class Of Warrant Or Right Common Stock Exchange Ratio

No definition available.

Name:	ptla_ClassOfWarrantOrRightCommonStockExchangeRatio
Namespace Prefix:	ptla_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant