v3.25.1

Commitments and Contingencies (Narrative) (Details)				12 Months Ended
Commitments and Contingencies (Narrative) (Details)	Jun. 28, 2024 USD ($)	Jun. 15, 2023 USD ($) ft²	Oct. 27, 2017 USD ($) ft²	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jun. 14, 2023 ft²	Jun. 14, 2022 USD ($) ft²
Commitments and Contingencies
Leased area (in square feet) \| ft²		11,916	27,043			26,503	26,503
Total base rent, net of abatements			$ 3,600,000
Total abatements			600,000
Security deposit			800,000
Security deposit, fully-occupied			1,300,000
Operating lease liability				$ 878,000	$ 2,500,000		$ 2,200,000
Operating lease right-of-use asset, net				81,000	1,566,000		$ 2,200,000
Adjustment to right of use asset		$ 1,000,000
Adjustment to operating lease liability		1,200,000
Gain on modification of sublease		$ 200,000		$ 314,000	$ 220,000
Termination fee	$ 40,000
Letter of Credit
Commitments and Contingencies
Security deposit			500,000
Security deposit, fully-occupied			1,000,000
Cash
Commitments and Contingencies
Security deposit			300,000
Security deposit, fully-occupied			$ 300,000

Amount of gain (loss) on modification of lease before expiration of lease term.

+ References

No definition available.

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Balance Type:	credit
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- Definition

Amount of increase (decrease) in obligation for right to use lease.

+ References

No definition available.

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- Definition

The total abatements for the operating lease over the lease term.

+ References

No definition available.

+ Details

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Namespace Prefix:	mbio_
Data Type:	xbrli:monetaryItemType
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- Definition

The total base rent, net of abatements, for the operating lease over the lease term.

+ References

No definition available.

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Namespace Prefix:	mbio_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

The amount of security deposit required when the facility is fully-occupied by the lessee.

+ References

No definition available.

+ Details

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

- Definition

Amount of gain (loss) on termination of lease before expiration of lease term.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 40
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479092/842-20-40-1

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- Definition

Amount of increase (decrease) in obligation for operating lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 230
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (g)(1)
-SubTopic 20
-Topic 842
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-4

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- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 7A
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-7A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

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Data Type:	xbrli:stringItemType
Balance Type:	na
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- Definition

Net rentable area for properties owned.

+ References

No definition available.

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Data Type:	dtr-types:areaItemType
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- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

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

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

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

- Definition

The amount of an asset, typically cash, provided to a counterparty to provide certain assurance of performance by the entity pursuant to the terms of a written or oral agreement, such as a lease.

+ 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(17))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

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