Collaboration, License, Co-Promotion and Other Commercial Agreements - Other Collaborations and License Agreements (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Collaboration, License and Co-Promotion Agreements
Research and development	$ 33,702	$ 31,842
Agreement One - other collaboration and license agreements \| Development milestones
Collaboration, License and Co-Promotion Agreements
Contingent milestone payable	7,500
Milestone payment made	2,500
Agreement One - other collaboration and license agreements \| Regulatory milestones
Collaboration, License and Co-Promotion Agreements
Contingent milestone payable	18,000
Milestone payment made	0
Agreement Two - other collaboration and license agreements
Collaboration, License and Co-Promotion Agreements
Contingent milestone payable per product, maximum	114,500
Agreement Two - other collaboration and license agreements \| Sales milestones
Collaboration, License and Co-Promotion Agreements
Contingent milestone payable per product	35,000
Agreement Two - other collaboration and license agreements \| Development milestones
Collaboration, License and Co-Promotion Agreements
Contingent milestone payable per product	21,500
Agreement Two - other collaboration and license agreements \| Regulatory milestones
Collaboration, License and Co-Promotion Agreements
Contingent milestone payable per product	$ 58,000

Represents the amount of milestone paid under the collaboration agreements.

No definition available.

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

- Definition

Represents the amount of contingent milestone payments payable by the entity upon achievement of certain development and commercialization milestones.

+ References

No definition available.

+ Details

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

- Definition

Represents the maximum amount of contingent milestone payable by the Company (per product) upon achievement of certain development and commercialization milestones.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of contingent milestone payable by the Company (per product) upon achievement of certain development and commercialization milestones.

+ References

No definition available.

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 730
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6420194&loc=d3e21568-108373

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 985
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6501960&loc=d3e128462-111756

+ Details

Name:	us-gaap_ResearchAndDevelopmentExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_TypeOfArrangementAxis=irwd_OtherCollaborationAndLicenseAgreementsNumberOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	irwd_AchievementOfMilestoneAxis=irwd_DevelopmentMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	irwd_AchievementOfMilestoneAxis=irwd_RegulatoryMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=irwd_OtherCollaborationAndLicenseAgreementsNumberTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	irwd_AchievementOfMilestoneAxis=irwd_SalesMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: