Employee Stock Benefit Plans - Share-based Compensation Expense (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($)
Employee Stock Benefit Plans
Share-based compensation expense, other modifications	$ 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