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Represents the potential fee receivable for each license exercised under the collaborative agreement.

No definition available.

Name:	imgn_CollaborativeArrangementExerciseFeePotentialPerLicense
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Represents the estimated term of licenses under the collaborative arrangements.

No definition available.

Name:	imgn_CollaborativeArrangementLicensesEstimatedTerm
Namespace Prefix:	imgn_
Data Type:	xbrli:durationItemType
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Represents the amount of potential payments that could be received under the collaborative agreement.

No definition available.

Name:	imgn_CollaborativeArrangementMilestonePaymentsPotential
Namespace Prefix:	imgn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Revenue from multiple-deliverable arrangements that include milestone and licensing fees revenue. Milestone revenue is consideration received upon achieving contractual goals. Licensing revenue is consideration received from another party for the right to use, but not own, certain of the entity's intangible assets.

No definition available.

Name:	imgn_LicenseAndMilestoneFees
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Represents the number of single-target licenses the company has right to use.

No definition available.

Name:	imgn_NumberOfSingleTargetLicenses
Namespace Prefix:	imgn_
Data Type:	xbrli:integerItemType
Balance Type:	na
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- Details

Name:	us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
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Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

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Cash received from collaborators during the current period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585