Commitments and Contingencies - Capital Leases (Details) - Vehicles - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Jun. 30, 2018
Lease Commitments
Capital lease, term	12 months
Letters of credit securing capital lease obligations		$ 0.6
Weighted average interest rate on the outstanding capital lease obligations (as a percent)		3.50%

Term of lessee's capital lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

No definition available.

Name:	irwd_LesseeCapitalLeaseTermOfContract
Namespace Prefix:	irwd_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration