Gain (Loss) On Extinguishment Of Royalty Monetization Liability

No definition available.

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Namespace Prefix:	mgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Liability Related To Future Royalties, Amount Recognized At Fair Value Upon Amendment

+ References

No definition available.

+ Details

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

- Definition

Liability Related To Future Royalties, Derecognition Upon Amendment

+ References

No definition available.

+ Details

Name:	mgnx_LiabilityRelatedToFutureRoyaltiesDerecognitionUponAmendment
Namespace Prefix:	mgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Liability related to future royalty [Line Items]

+ References

No definition available.

+ Details

Name:	mgnx_LiabilityRelatedToFutureRoyaltyLineItems
Namespace Prefix:	mgnx_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Proceeds from sale of future royalties

+ References

No definition available.

+ Details

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

- Definition

Royalty Monetization Arrangement, Aggregate Purchase Price Multiple, Maximum

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Royalty Monetization Arrangement, Aggregate Purchase Price Multiple, Minimum

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

Royalty Monetization Arrangement, Contingent Payment Receivable

+ References

No definition available.

+ Details

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Namespace Prefix:	mgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Royalty Monetization Arrangement, Interest Rate, Effective Percentage

+ References

No definition available.

+ Details

Name:	mgnx_RoyaltyMonetizationArrangementInterestRateEffectivePercentage
Namespace Prefix:	mgnx_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Royalty Monetization Arrangement, Royalty Payment Threshold

+ References

No definition available.

+ Details

Name:	mgnx_RoyaltyMonetizationArrangementRoyaltyPaymentThreshold
Namespace Prefix:	mgnx_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of interest expense classified as nonoperating.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476153/220-40-55-4

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 220
-SubTopic 40
-Name Accounting Standards Codification
-Section 55
-Paragraph 14
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147476153/220-40-55-14

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-22

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483621/220-10-S99-2

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Royalty Monetization Arrangement - Narrative (Details) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended		11 Months Ended
	May 01, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	May 01, 2026 USD ($)
Liability related to future royalty [Line Items]
Non-cash loss on extinguishment of royalty monetization liability			$ 52,762	$ 0	$ 52,762	$ 0
Royalty Monetization Arrangement
Liability related to future royalty [Line Items]
Effective interest rate			7.40%		7.40%
Sagard Healthcare Partners \| Royalty Monetization Arrangement
Liability related to future royalty [Line Items]
Proceeds from sale of future royalties	$ 60,000	$ 70,000			$ 0	70,000	$ 130,000
Royalty payment threshold		$ 140,000		$ 140,000		140,000
Aggregate purchase price multiple, minimum	1.7						1.7
Aggregate purchase price multiple, maximum	2						2
Contingent payment receivable	$ 20,000						$ 20,000
Derecognition of original liability upon extinguishment	68,200				68,238	0
New liability recognized at fair value upon extinguishment	$ 181,000				181,000	0
Non-cash loss on extinguishment of royalty monetization liability			$ 52,800		52,800
Non-cash interest expense recognized			$ 4,000		$ 8,880	$ 587