Amortization Period Excess of Loss Reinsurance Coverage

No definition available.

Name:	mtg_AmortizationPeriodExcessofLossReinsuranceCoverage
Namespace Prefix:	mtg_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance, Quota Share Reinsurance Agreement, Terms, Annual Loss Ratio Cap

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsAnnualLossRatioCap
Namespace Prefix:	mtg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Reinsurance, Quota Share Reinsurance Agreement, Terms, Ceding Commission, Percent

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsCedingCommissionPercent
Namespace Prefix:	mtg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance, Quota Share Reinsurance Agreement, Terms, Contingent Termination Fee

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsContingentTerminationFee
Namespace Prefix:	mtg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reinsurance, Quota Share Reinsurance Agreement, Terms, Lifetime Loss Ratio Cap

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsLifetimeLossRatioCap
Namespace Prefix:	mtg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Reinsurance, Quota Share Reinsurance Agreement, Terms, Quota Share, Percent

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsQuotaSharePercent
Namespace Prefix:	mtg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance, Quota Share Reinsurance Agreement, Terms, Threshold For Private Mortgage Insurer Eligibility Requirements For Termination Election

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsThresholdForPrivateMortgageInsurerEligibilityRequirementsForTerminationElection
Namespace Prefix:	mtg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Reinsurance Retention Policy, Percent Of Total Trust Assets Invested In Cash Or Direct U.S. Federal Government Obligations

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceRetentionPolicyPercentOfTotalTrustAssetsInvestedInCashOrDirectU.S.FederalGovernmentObligations
Namespace Prefix:	mtg_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of earned premiums ceded to other entities.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17(Column C))
-URI http://asc.fasb.org/extlink&oid=120401096&loc=d3e574992-122915

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(1))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=84167274&loc=d3e27175-158546

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

+ Details

Name:	us-gaap_CededPremiumsEarned
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Definition

Ratio of non-life losses and loss expenses to non-life net premiums earned.

+ References

No definition available.

+ Details

Name:	us-gaap_LossRatio
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=99404803&loc=d3e21412-158489

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=99397103&loc=d3e6824-158387

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 3
-Subparagraph (cc)
-URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437

+ Details

Name:	us-gaap_ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to and paid by the ceding insurer.

+ References

+ Details

Name:	us-gaap_ReinsuranceRecoverablesOnPaidLosses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ReinsurancePolicyTypeAxis=mtg_CreditUnionQuotaShareReinsuranceAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ReinsurancePolicyTypeAxis=mtg_ExcessofLossReinsuranceAgreementsHomeReEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreement2023Member
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_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreements20172018Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Reinsurance - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Reinsurance - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effects of Reinsurance [Line Items]
Reinsurance recoverable on paid losses	$ 36,275			$ 36,275	$ 669
Reinsurance recoverable on loss reserves	$ 66,905			66,905	95,042	$ 21,641	$ 33,328
Ceded premiums earned				$ 163,031	188,729	129,337
Quota Share Reinsurance Agreements
Effects of Reinsurance [Line Items]
Ceding commission, percentage				20.00%
Annual loss ratio cap	300.00%			300.00%
Lifetime loss ratio cap	200.00%			200.00%
Threshold for private mortgage insurer eligibility requirements for termination election				90.00%
Contingent termination fee				$ 0
Reinsurance recoverable on loss reserves	$ 66,900			$ 66,900	95,000
Credit Union QSR
Effects of Reinsurance [Line Items]
Quota Share %				65.00%
Annual loss ratio				50.00%
Threshold for private mortgage insurer eligibility requirements for termination election				80.00%
Excess of Loss Reinsurance Agreements, Home Re Entities
Effects of Reinsurance [Line Items]
Ceded premiums earned				$ 44,500	$ 20,800	$ 17,600
Excess of Loss Reinsurance Agreements, Home Re Entities \| Minimum
Effects of Reinsurance [Line Items]
Amortization period excess of loss reinsurance coverage				10 years
Excess of Loss Reinsurance Agreements, Home Re Entities \| Maximum
Effects of Reinsurance [Line Items]
Amortization period excess of loss reinsurance coverage				12 years 6 months
Quota Share Reinsurance Agreement, 2023 \| Forecast
Effects of Reinsurance [Line Items]
Quota Share %		15.00%	15.00%
Annual loss ratio			62.00%
Quota Share Reinsurance Agreements, 2017 & 2018
Effects of Reinsurance [Line Items]
Contingent termination fee	5,000
Reinsurance recoverable on paid losses	$ 36,000			$ 36,000
Home Re special purpose insurers
Effects of Reinsurance [Line Items]
Percent of total trust assets invested in cash or direct U.S. federal government obligations				99.50%