Name:	mtg_NumberOfJurisdictionsWithRiskToCapitalRequirements
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The percentage of statutory policyholders' surplus, as defined, as of the preceding calendar year end which is used in the determination of the maximum allowable dividends that the insurance subsidiaries may pay in any twelve-month period without regulatory approval by the Office of the Commissioner of Insurance of the State of Wisconsin.

No definition available.

Name:	mtg_PercentageOfStatutoryPolicyholdersSurplusUsedToDetermineMaximumAllowableDividends
Namespace Prefix:	mtg_
Data Type:	dtr-types1:percentItemType
Balance Type:	na
Period Type:	instant

Statutory Accounting Practices, Statutory Amount Available For Dividend Payments Without Regulatory Approval, Measurement, Measurement Period

No definition available.

Name:	mtg_StatutoryAccountingPracticesStatutoryAmountAvailableForDividendPaymentsWithoutRegulatoryApprovalMeasurementMeasurementPeriod
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Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval, Measurement, Dividend Payment Period

No definition available.

Name:	mtg_StatutoryAccountingPracticesStatutoryAmountAvailableforDividendPaymentswithoutRegulatoryApprovalMeasurementDividendPaymentPeriod
Namespace Prefix:	mtg_
Data Type:	xbrli:durationItemType
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- References

No definition available.

Name:	mtg_StatutoryCapitalRequirementsAbstract
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Statutory Capital Requirements, Risk To Capital Ratio

No definition available.

Name:	mtg_StatutoryCapitalRequirementsRiskToCapitalRatio
Namespace Prefix:	mtg_
Data Type:	xbrli:pureItemType
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Period Type:	instant

For insurance companies, a description of the minimum regulatory capital requirements imposed by state insurance regulators, and restrictions on dividend payments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477908/944-505-50-1