Employee Stock Benefit Plans - Share-based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2019
Employee Stock Benefit Plans
Share-based compensation expense, other modifications	$ 0.0	$ 2.4

Allocated Share-based Compensation Expense, Other Modifications

No definition available.

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