Estimated development cost sharing reoverable through earnings.

No definition available.

Name:	meip_EstimatedDevelopmentCostSharingRecoverableThroughEarnings
Namespace Prefix:	meip_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Expected milestone payment receivable.

+ References

No definition available.

+ Details

Name:	meip_ExpectedMilestonePaymentReceivable
Namespace Prefix:	meip_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

License obligation account transaction price allocated.

+ References

No definition available.

+ Details

Name:	meip_LicenseObligationAccountTransactionPriceAllocated
Namespace Prefix:	meip_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Payment for license agreement.

+ References

No definition available.

+ Details

Name:	meip_PaymentForLicenseAgreement
Namespace Prefix:	meip_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Potential milestone payments receivable.

+ References

No definition available.

+ Details

Name:	meip_PotentialMilestonePaymentsReceivable
Namespace Prefix:	meip_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Total transaction price in respect of colloboration revenue.

+ References

No definition available.

+ Details

Name:	meip_TotalTransactionPriceInRespectOfColloborationRevenue
Namespace Prefix:	meip_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Total upfront payment receivable for grant of rights.

+ References

No definition available.

+ Details

Name:	meip_TotalUpfrontPaymentReceivableForGrantOfRights
Namespace Prefix:	meip_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Up Front Payment

+ References

No definition available.

+ Details

Name:	meip_UpFrontPayment
Namespace Prefix:	meip_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 2
-URI https://asc.fasb.org/extlink&oid=126919976&loc=SL49130532-203044

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=126919976&loc=SL49130531-203044

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130549-203045

+ Details

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

- Definition

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 8
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130549-203045

+ Details

Name:	us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix:	us-gaap_
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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(26)(c))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Carrying amount as of the balance sheet date of obligations due all related parties.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(k)(1))
-URI https://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iii)(C))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(5))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.17)
-URI https://asc.fasb.org/extlink&oid=126734703&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iv))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(4)(iii)(B))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1A
-Subparagraph (SX 210.13-01(a)(5))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442526-122756

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section S99
-Paragraph 1B
-Subparagraph (SX 210.13-02(a)(4)(iv))
-URI https://asc.fasb.org/extlink&oid=126975872&loc=SL124442552-122756

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(3),(4))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI https://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

Name:	us-gaap_DueToRelatedPartiesCurrentAndNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of transaction price allocated to performance obligation that has not been recognized as revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126920106&loc=SL49130556-203045

+ Details

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

- Details

Name:	dei_LegalEntityAxis=meip_KyowaKirinCoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=meip_PresageBiosciencesIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=meip_IncrementalPaymentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=meip_PotentialPaymentsOnAchievementOfDevelopmentRegulatoryAndCommercialMilestonesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_ProductOrServiceAxis=meip_ExUsLicenseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=meip_DevelopmentServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

License Agreements - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	6 Months Ended
	Sep. 30, 2017	Dec. 31, 2022	Dec. 31, 2021	Jun. 30, 2022	May 31, 2020
Related Party Transaction [Line Items]
Revenue recognized		$ (2,831)	$ (1,264)
Kyowa Kirin Co
Related Party Transaction [Line Items]
Total upfront payment receivable for grant of rights					$ 100,000
Presage License Agreement \| Presage Biosciences, Inc.
Related Party Transaction [Line Items]
Compensation payable for grant of rights	$ 4,900
Payment for license	2,900
Presage License Agreement \| Presage Biosciences, Inc. \| Incremental Payment
Related Party Transaction [Line Items]
Compensation payable for grant of rights	2,000
Presage License Agreement \| Presage Biosciences, Inc. \| Potential Payments on Achievement of Development Regulatory and Commercial Milestones
Related Party Transaction [Line Items]
Milestone payment receivable amount	$ 179,000
Kkc Agreements [Member] \| Kyowa Kirin Co
Related Party Transaction [Line Items]
Upfront payment		100,000
Transaction price relating to the performance obligation		216,300
Expected milestone payment receivable		20,000
Estimated development cost sharing recovered through earnings		91,100
Deferred revenue		5,200
Revenue recognized		16,600
Revenue related to non-refundable payments for performance obligations		8,600
Kkc Agreements [Member] \| Kyowa Kirin Co \| Ex US License
Related Party Transaction [Line Items]
Revenue recognized		21,000
License Obligation Account Transaction Price Allocated		64,500
Kkc Agreements [Member] \| Kyowa Kirin Co \| Development Services
Related Party Transaction [Line Items]
Contract with customer liability non current		2,900		$ 30,900
Kkc Agreements [Member] \| Kyowa Kirin Co \| Maximum
Related Party Transaction [Line Items]
Estimated development cost sharing recovered through earnings		$ 143,800