Fair Value Measurements (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Cash proceeds realized from maturities	$ 2,600
Redemptions of securities available-for-sale	$ 13,828

The amount of proceeds from redemption of marketable debt securities, available-for-sale

No definition available.

Name:	tara_ProceedsFromRedemptionOfMarketableDebtSecuritiesAvailableforsale
Namespace Prefix:	tara_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration