Fair Value of Financial Instruments - Transfers Between Fair Value Measurement Levels (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019
Fair value transfers
Fair value transfer between measurement levels	$ 0	$ 0

Amount of transfers measured on recurring basis between measurement levels.

No definition available.

Name:	irwd_FairValueTransferBetweenMeasurementLevels
Namespace Prefix:	irwd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration