Schedule of Changes in Estimated Fair Value of Warrant Liability (Detail) - USD ($) $ in Thousands	3 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Fair value measurements Significant unobservable inputs [Line Items]
Beginning balance	$ 22,355
Change in estimated fair value of liability classified warrants	2,587	$ 13,224
Ending balance	19,768
Fair Value, Measurements, Recurring [Member] \| Level 3
Fair value measurements Significant unobservable inputs [Line Items]
Beginning balance	22,355	40,483
Change in estimated fair value of liability classified warrants	(2,587)	(13,224)
Ending balance	$ 19,768	$ 27,259

Fair Value Measurements, Significant Unobservable Inputs [Line Items]

No definition available.

Name:	meip_FairValueMeasurementsSignificantUnobservableInputsLineItems
Namespace Prefix:	meip_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of unrealized gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3) and still held.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

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

- Definition

Fair value portion of warrants not settleable in cash classified as equity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123874694&loc=d3e19207-110258

+ Details

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

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: