Financial Instruments - Additional Information (Detail)	12 Months Ended
Dec. 31, 2016
Investments Debt And Equity Securities [Abstract]
Available For Sale Securities Contractual Maturity	1 year

Available for sale securities maximum remaining contractual maturity.

No definition available.

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Namespace Prefix:	ptla_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration