Collaboration, License, Co-Promotion and Other Commercial Agreements - North America - General Information (Details) - North America - Collaborative arrangement $ in Millions	3 Months Ended
Mar. 31, 2018 USD ($) item payment	Mar. 31, 2017 USD ($)
Sales milestones
Collaboration, License and Co-Promotion Agreements
Sales-related milestone if certain conditions are met	$ 100.0
Allergan
Collaboration, License and Co-Promotion Agreements
Equity investment in the entity's capital stock	25.0
Net cost sharing offset or incremental expense related to research and development expense	1.4	$ 1.4
Cost sharing amount, reduction to research and development	$ 0.4	$ 0.4
Remaining commercial-period performance obligations \| item	3
Allergan \| Development milestones
Collaboration, License and Co-Promotion Agreements
Cumulative license fees and development milestone payments received	$ 205.0
Number of milestone payments received \| payment	6
Allergan \| Sales milestones
Collaboration, License and Co-Promotion Agreements
Percentage of net profit from commercialization (as a percent)	50.00%
Percentage of net loss from commercialization (as a percent)	50.00%

Represents the percentage of net loss from commercialization.

No definition available.

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Namespace Prefix:	irwd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of net profit from commercialization.

+ References

No definition available.

+ Details

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Namespace Prefix:	irwd_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Contingent sales-related milestone receivable.

+ References

No definition available.

+ Details

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Namespace Prefix:	irwd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the reduction to research and development expense for the amount received from the collaboration partner under cost sharing provisions.

+ References

No definition available.

+ Details

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Namespace Prefix:	irwd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the cumulative amount of license fees and milestone payments received to date.

+ References

No definition available.

+ Details

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Namespace Prefix:	irwd_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents net cost sharing offset amounts related to collaborative arrangement where a cost sharing agreement exists for research and development expenses. Amounts may net to either a reduction of expense, or may net to increased expense.

+ References

No definition available.

+ Details

Name:	irwd_NetCostSharingOffsetRelatedToResearchAndDevelopmentExpenseReimbursement
Namespace Prefix:	irwd_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of milestone payments received.

+ References

No definition available.

+ Details

Name:	irwd_NumberOfMilestonePaymentsReceived
Namespace Prefix:	irwd_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Remaining Commercial Period Performance Obligations.

+ References

No definition available.

+ Details

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Namespace Prefix:	irwd_
Data Type:	xbrli:integerItemType
Balance Type:	na
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

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

- Definition

Proceeds from issuance of capital stock which provides for a specific dividend that is paid to the shareholders before any dividends to common stockholders and which takes precedence over common stockholders in the event of liquidation.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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Namespace Prefix:
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- Details

Name:	us-gaap_TypeOfArrangementAxis=us-gaap_CollaborativeArrangementMember
Namespace Prefix:
Data Type:	na
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- Details

Name:	irwd_AchievementOfMilestoneAxis=irwd_SalesMilestonesMember
Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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