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 cash inflow from parent to increase statutory capital.

No definition available.

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

The insurance in force multiplied by the insurance coverage percentage.

No definition available.

Name:	mtg_DirectDomesticPrimaryRiskInForce
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 new insurance written during the current period that was written in jurisdictions that have risk-to-capital requirements.

No definition available.

Name:	mtg_PercentageNewInsuranceWrittenJurisdictionsWithRiskToCapitalRequirements
Namespace Prefix:	mtg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

The percentage of surplus as regards policyholders allowed for determining the amount of admitted statutory deferred tax assets.

No definition available.

Name:	mtg_PercentageOfSurplusAsRegardsPolicyholders
Namespace Prefix:	mtg_
Data Type:	num: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:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

The risk-to-capital ratio of the entity's combined insurance operations, including its reinsurance affiliates, as of the end of the reporting period.

No definition available.

Name:	mtg_RiskToCapitalRatioOfCombinedInsuranceOperationsIncludingReinsuranceAffiliatesAtEndOfPeriod
Namespace Prefix:	mtg_
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

The sum of the tax effects as of the balance sheet date of the admitted amounts of all future tax deductions arising from temporary differences between tax basis and statutory accounting principles basis recognition of assets, liabilities, revenues and expenses.

No definition available.

Name:	mtg_StatutoryDeferredTaxAssetsAdmitted
Namespace Prefix:	mtg_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 505

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 60

-Subparagraph h

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

- Details

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- Details

Name:	us-gaap_RelatedPartyTransactionLineItems
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Period Type:	duration

The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against short-term borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. For a classified balance sheet represents the current portion only (the noncurrent portion has a separate concept); there is a separate and distinct element for unclassified presentations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 80

-Subparagraph Exhibit 4-8, 3

-IssueDate 2006-05-01

-Chapter 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.1)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 1

-Article 5

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

The amount of statutory capital and surplus (stockholders' equity) as of the balance sheet date using prescribed or permitted statutory accounting practices (rather than GAAP, if different) of the state or country.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 60

-Paragraph 60

-Subparagraph h

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 94-5

-Paragraph 8, 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.23(c))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 505

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6486098&loc=d3e24708-158529

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 24

-Subparagraph c

-Article 7