Face (par) amount of debt instrument at time of issuance.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Face (par) amount of the original debt instrument that was repurchased.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentRepurchasedFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermDebtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_NotesPayableOtherPayablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=irwd_Notes8.375PercentDue2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Data Type:	na
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- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_ConvertibleNotesPayableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=irwd_ConvertibleSeniorNotes2.25PercentDue2022Member
Namespace Prefix:
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- Details

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Data Type:	na
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- Details

Name:	us-gaap_DebtInstrumentAxis=irwd_ConvertibleSeniorNotes0.75PercentDue2024Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=irwd_ConvertibleSeniorNotes1.50PercentDue2026Member
Namespace Prefix:
Data Type:	na
Balance Type:
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Fair Value of Financial Instruments - Notes Payable (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 16, 2019	Aug. 31, 2019	Aug. 12, 2019	Dec. 31, 2018	Sep. 23, 2016	Jun. 30, 2015
Notes Payable \| 8.375% Notes due 2026
Fair value disclosures
Stated interest rate (as a percent)	8.375%					8.375%
Debt Instrument, Repurchased Face Amount		$ 116,500
Aggregate principal amount of notes issued						$ 150,000
Notes Payable \| 8.375% Notes due 2026 \| Significant Unobservable Inputs (Level 3)
Fair value disclosures
Estimated fair value					$ 148,200
Convertible Senior Notes \| 2.25% Convertible Senior Notes due 2022
Fair value disclosures
Stated interest rate (as a percent)		2.25%					2.25%
Debt Instrument, Repurchased Face Amount		$ 215,000	$ 215,000
Aggregate principal amount of notes issued	$ 120,699				335,699		$ 335,700
Convertible Senior Notes \| 2.25% Convertible Senior Notes due 2022 \| Significant Other Observable Inputs (Level 2)
Fair value disclosures
Estimated fair value	120,000				$ 315,000
Convertible Senior Notes \| 0.75% Convertible Senior Notes due 2024
Fair value disclosures
Stated interest rate (as a percent)				0.75%
Aggregate principal amount of notes issued	200,000		200,000	$ 200,000
Convertible Senior Notes \| 0.75% Convertible Senior Notes due 2024 \| Significant Other Observable Inputs (Level 2)
Fair value disclosures
Estimated fair value	185,900
Convertible Senior Notes \| 1.50% Convertible Senior Notes due 2026
Fair value disclosures
Stated interest rate (as a percent)				1.50%
Aggregate principal amount of notes issued	200,000		$ 200,000	$ 200,000
Convertible Senior Notes \| 1.50% Convertible Senior Notes due 2026 \| Significant Other Observable Inputs (Level 2)
Fair value disclosures
Estimated fair value	$ 183,600