Fair Value of Financial Instruments - Transfers Between Fair Value Measurement Levels (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair value transfers
Fair value transfer between measurement levels	$ 0	$ 0	$ 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