Subsequent Events - Derivatives (Details) - Subsequent Event - Forecast - Oil Costless Collars bbl in Millions	12 Months Ended
Dec. 31, 2027 $ / barrel bbl	Dec. 31, 2026 $ / barrel bbl
Subsequent Event [Line Items]
Notional volume (in barrels) \| bbl	2.7	3.2
Weighted-average floor price (in dollars per barrel)	70.00	72.14
Weighted-average ceiling price (in dollars per barrel)	83.28	91.09

The average cap rate on a group of price risk derivatives such as caps or collars. A payment or receipt is triggered if the market rate exceeds the cap rate on the contract.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-5

+ Details

Name:	us-gaap_DerivativeAverageCapPrice
Namespace Prefix:	us-gaap_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

The average floor rate on a group of price risk derivatives such as floors or collars. A payment or receipt is triggered if the market rate falls below the floor rate on the contract.

+ References

+ Details

Name:	us-gaap_DerivativeAverageFloorPrice
Namespace Prefix:	us-gaap_
Data Type:	srt-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

Nominal volume used to calculate payments on a derivative instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 181
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-181

+ Details

Name:	us-gaap_DerivativeNonmonetaryNotionalAmountVolume
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:volumeItemType
Balance Type:	na
Period Type:	duration

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 830
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481674/830-30-50-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 855
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483399/855-10-50-2

+ Details

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

- Details

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

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=mgy_OilCostlessCollarsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: