Name:	mtg_DefinedBenefitPlanBenefitsPaidFromFundLumpSum
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The future earnings period, in years, used in determining the average rate of earnings expected on the classes of funds invested or to be invested to provide for the benefits of the plans. This was then used in selecting the expected long-term rate of return on assets included in the actuarial assumptions used in the valuation of projected benefit obligations, net periodic benefit costs and accumulated postretirement benefit obligation.

No definition available.

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The maximum investment in international mutual funds, as a percentage of the equity investments range, to total plan assets as of the measurement date of the latest statement of financial position.

No definition available.

Name:	mtg_DefinedBenefitPlanMaximuminvestmentininternationalmutualfunds
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Period Type:	duration

The minimum value of outstanding noncallable bonds used in a hypothetical cash flow bond matching exercise for purposes of selecting a discount rate related to actuarial assumptions used in the valuation of projected benefit obligations, net periodic benefit costs and accumulated postretirement benefit obligation.

No definition available.

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The company's discretionary profit sharing contribution as a percentage of each participant's eligible compensation.

No definition available.

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Data Type:	num:percentItemType
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The minimum percentages that return should exceed growth in consumer price index annually.

No definition available.

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Data Type:	num:percentItemType
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Period Type:	duration

Represents minimum percentages of gain loss consider for amortization.

No definition available.

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Data Type:	num:percentItemType
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The investment in international mutual funds primarily based in Europe and the Pacific Basin, as a percentage of the equity investments range.

No definition available.

Name:	mtg_PercentofinternationalmutualfundsequityallocationincompaniesprimarilybasedinEuropeandPacificBasin
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The investment in international mutual funds (emerging markets), as a percentage of the equity investments range.

No definition available.

Name:	mtg_Percentofinternationalmutualfundsequityallocationinemergingmarkets
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Data Type:	num:percentItemType
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Period Type:	instant

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.

No definition available.

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Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 55
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

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Period Type:	instant

Amount of cost for defined contribution plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

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Data Type:	xbrli:monetaryItemType
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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

No definition available.

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Data Type:	num:percentItemType
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Period Type:	duration

Percentage employer matches of the employee's percentage contribution matched.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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Name:	us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis=us-gaap_DefinedBenefitPlanEquitySecuritiesMember
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