Milestone additional payments receivable post option exercise.

No definition available.

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Namespace Prefix:	mtem_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Milestone payments receivable post option exercise.

+ References

No definition available.

+ Details

Name:	mtem_MilestonePaymentsReceivablePostOptionExercise
Namespace Prefix:	mtem_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of product and development grant awarded.

+ References

No definition available.

+ Details

Name:	mtem_ProductDevelopmentGrantAward
Namespace Prefix:	mtem_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reimbursement amounts submitted in excess of amounts received are recorded as receivables.

+ References

No definition available.

+ Details

Name:	mtem_ReimbursementAmountsReceivedInExcessOfGrantRecordedAsReceivables
Namespace Prefix:	mtem_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Research and development collaboration agreements.

+ References

No definition available.

+ Details

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Namespace Prefix:	mtem_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Transaction price allocated to performance obligations.

+ References

No definition available.

+ Details

Name:	mtem_TransactionPriceAllocatedToPerformanceObligations
Namespace Prefix:	mtem_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Upfront payment.

+ References

No definition available.

+ Details

Name:	mtem_UpfrontPayment
Namespace Prefix:	mtem_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(26)(c))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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

- Definition

Amount of deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable, classified as current.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(20))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of deferred income and obligation to transfer product and service to customer for which consideration has been received or is receivable, classified as noncurrent.

+ References

+ Details

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

- Definition

Carrying amount as of the balance sheet date of amounts due under the terms of governmental, corporate, or foundation grants. For classified balance sheets, represents the current amount receivable, that is amounts expected to be collected within one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(3)(a)(4))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

+ Details

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

- Definition

Amount of revenue from collaborative arrangement. Excludes revenue from contract with customer under Topic 606.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 808
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479402/808-10-50-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 3
-SubTopic 10
-Topic 808
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479428/808-10-45-3

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Balance Type:
Period Type:

- Details

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

- Details

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Period Type:

- Details

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- Details

Name:	srt_RangeAxis=srt_MaximumMember
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Namespace Prefix:
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Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=mtem_CancerResearchGrantContractMember
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Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
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- Details

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- Details

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RESEARCH AND DEVELOPMENT AGREEMENTS (Detail) - USD ($)	1 Months Ended		3 Months Ended
RESEARCH AND DEVELOPMENT AGREEMENTS (Detail) - USD ($)	Feb. 28, 2021	Sep. 30, 2018	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			$ 11,086,000	$ 36,629,000
Deferred revenue, current					$ 9,031,000
Grants revenue receivable			412,000		250,000
Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			10,924,000	33,627,000
Bristol Myers Squibb Collaboration Agreement \| License Agreement Terms [Member] \| Bristol Myers Squibb
Research And Development Collaboration Agreements [Line Items]
Upfront payment	$ 70,000,000.0
Transaction price allocated to performance obligations	70,000,000.0
Deferred revenue, current			0		9,000,000.0
Deferred revenue, non-current			0		0
Bristol Myers Squibb Collaboration Agreement \| License Agreement Terms [Member] \| Bristol Myers Squibb \| Maximum
Research And Development Collaboration Agreements [Line Items]
Milestone payments receivable if option is exercised	874,500,000
Additional milestone payments receivable if option is exercised	$ 450,000,000.0
Bristol Myers Squibb Collaboration Agreement \| License Agreement Terms [Member] \| Bristol Myers Squibb \| Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			10,900,000	33,600,000
Bristol Myers Squibb Collaboration Agreement \| License Agreement Terms, Target Completion \| Bristol Myers Squibb \| Research and development revenue
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			10,900,000	25,800,000
CPRIT Agreement \| Additional Funding Agreement Terms \| Cancer Prevention and Research Institute of Texas \| Grant
Research And Development Collaboration Agreements [Line Items]
Revenue from collaborative arrangement			14,300,000
Deferred revenue			0		0
Product development grant awarded		$ 15,200,000
Reimbursement amounts submitted in excess of amounts received are recorded as receivables			200,000	$ 3,000,000.0
Grants revenue receivable			$ 400,000		$ 300,000