Additional extended lease term.

No definition available.

Name:	mtem_AdditionalExtendedLeaseTerm
Namespace Prefix:	mtem_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Additional extended lease term beginning date.

+ References

No definition available.

+ Details

Name:	mtem_AdditionalExtendedLeaseTermBeginningDate
Namespace Prefix:	mtem_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Additional extended lease term end date.

+ References

No definition available.

+ Details

Name:	mtem_AdditionalExtendedLeaseTermEndDate
Namespace Prefix:	mtem_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount abated in installments from monthly lease commitments.

+ References

No definition available.

+ Details

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

- Definition

Lease commitment amount.

+ References

No definition available.

+ Details

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

- Definition

Lease commitment period.

+ References

No definition available.

+ Details

Name:	mtem_LeaseCommitmentPeriod
Namespace Prefix:	mtem_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Option to extend lease term.

+ References

No definition available.

+ Details

Name:	mtem_OptionToExtendLeaseTerm
Namespace Prefix:	mtem_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Area of land held.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfLand
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:areaItemType
Balance Type:	na
Period Type:	instant

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

- Definition

Remaining lease term of operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseRemainingLeaseTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Term of lessee's operating lease renewal, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI https://asc.fasb.org/extlink&oid=128292326&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseRenewalTerm
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	srt_CounterpartyNameAxis=mtem_FourthAmendmentLeaseWithNWAustinOfficePartnersLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=stpr_NJ
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=stpr_TX
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
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Leases - Additional Information (Detail) $ in Millions	Oct. 18, 2022 USD ($)	Jul. 31, 2022	Sep. 30, 2022	Sep. 30, 2021 ft²
Lessee Lease Description [Line Items]
Lessee, operating leases renewal lease term			7 years
Lease Amendment \| Subsequent Event
Lessee Lease Description [Line Items]
Additional extended lease term	6 years
Additional extended lease term beginning date	Aug. 31, 2023
Additional extended lease term end date	Aug. 31, 2029
Committed lease amount payment period	6 years
Option to extend lease term	7 years
Aggregated lease commitments	$ 6.7
Amount abated in installments from the monthly lease commitments	$ 0.2
New Jersey
Lessee Lease Description [Line Items]
Area of Land \| ft²				10,000
Texas
Lessee Lease Description [Line Items]
Additional extended lease term		5 years
Additional extended lease term beginning date		Aug. 31, 2023
Additional extended lease term end date		Aug. 31, 2028
Minimum [Member]
Lessee Lease Description [Line Items]
Lessee, operating leases remaining lease term.			1 year
Maximum
Lessee Lease Description [Line Items]
Lessee, operating leases remaining lease term.			7 years