Name:	mtg_AmountOfPolicyholdersPositionAboveOrBelowRequiredRegulatoryMinimum
Namespace Prefix:	mtg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of minimum policyholder position (MPP) required by the entity's domiciliary state.

No definition available.

Name:	mtg_AmountOfRequiredMpp
Namespace Prefix:	mtg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The number of jurisdictions that require a mortgage insurer to maintain a minimum amount of statutory capital relative to the risk in force (or a similar measure) in order for the mortgage insurer to continue to write new business. This is generally referred to as a risk-to-capital requirement.

No definition available.

Name:	mtg_NumberOfJurisdictionsWithRiskToCapitalRequirements
Namespace Prefix:	mtg_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

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-types:percentItemType
Balance Type:	na
Period Type:	instant

The entity's risk-to-capital ratio as of the end of the reporting period.

No definition available.

Name:	mtg_Risktocapitalratioatendofperiod
Namespace Prefix:	mtg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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

No definition available.

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

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
Balance Type:	na
Period Type:	duration

- References

No definition available.

Name:	mtg_StatutoryCapitalRequirementsAbstract
Namespace Prefix:	mtg_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Statutory Capital Requirements, Risk To Capital Ratio

No definition available.

Name:	mtg_StatutoryCapitalRequirementsRiskToCapitalRatio
Namespace Prefix:	mtg_
Data Type:	xbrli:pureItemType
Balance Type:	na
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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 505
-Section 50
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529