XML 99 R79.htm IDEA: XBRL DOCUMENT
v3.22.4

Benefit Plans - Narrative (Details) - USD ($) $ in Thousands |  | 12 Months Ended
--- | --- | ---
Jan. 01, 2023 | Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Minimum percentages of gain loss consider for amortization (in hundredths) |  | 10.00% |  |
Minimum value of outstanding noncallable bonds used in hypothetical cash flow bond matching exercise |  | $ 50,000 |  |
Future earnings period used in determining the expected average rate of earnings |  | 20 years |  |
Discretionary profit sharing contribution as a percentage of participant's eligible compensation (in hundredths) |  | 5.00% |  |
Matching contribution rate on employees' contributions (in hundredths) |  | 100.00% |  |
Employee contributions subject to employer match (in hundredths) |  | 4.00% |  |
Profit sharing and 401(k) savings plan expenses |  | $ 7,600 | $ 8,000 | $ 8,000
Subsequent Event |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Matching contribution for first two percent, as a percent | 200.00% |  |  |
Matching contribution for the next two percent, as a percent | 100.00% |  |  |
Matching contribution, percent of employee's gross pay, first two percent contributed, as a percent | 2.00% |  |  |
Matching contribution, percent of employee's gross pay, next two percent contributed, as a percent | 2.00% |  |  |
Other Postretirement Benefit Plan |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Minimum percentage return should exceed growth in consumer price index annually (in hundredths) |  | 5.75% |  |
Maximum investment in international mutual funds (in hundredths) |  | 30.00% |  |
Percent of international mutual funds equity allocation in emerging markets (in hundredths) |  | 2.00% |  |
Percent of international mutual funds equity allocation in companies primarily based in Europe and the Pacific Basin (in hundredths) |  | 17.00% |  |
Company Contributions |  | $ 0 | 0 |
Pension and Supplemental Executive Retirement Plans |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Company Contributions |  | $ 6,414 | $ 7,162 |

X
- Definition 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. + References No definition available. + Details
Name: | mtg_DefinedBenefitPlanFutureEarningsPeriodUsedInDeterminingExpectedAverageRateOfEarnings
Namespace Prefix: | mtg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition 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. + References No definition available. + Details
Name: | mtg_DefinedBenefitPlanMaximuminvestmentininternationalmutualfunds
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition 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. + References No definition available. + Details
Name: | mtg_DefinedBenefitPlanMinimumValueOfOutstandingNoncallableBondsUsedInHypotheticalCashFlowBondMatchingExercise
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay, First Two Percent Contributed + References No definition available. + Details
Name: | mtg_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployeesGrossPayFirstTwoPercentContributed
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay, Next Two Percent Contributed + References No definition available. + Details
Name: | mtg_DefinedContributionPlanEmployerMatchingContributionPercentOfEmployeesGrossPayNextTwoPercentContributed
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Contribution Plan, Employer Matching Contribution, Percent of Match, First Two Percent Contributed + References No definition available. + Details
Name: | mtg_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchFirstTwoPercentContributed
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Defined Contribution Plan, Employer Matching Contribution, Percent of Match, Next Two Percent Contributed + References No definition available. + Details
Name: | mtg_DefinedContributionPlanEmployerMatchingContributionPercentOfMatchNextTwoPercentContributed
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The company's discretionary profit sharing contribution as a percentage of each participant's eligible compensation. + References No definition available. + Details
Name: | mtg_DiscretionaryProfitSharingContributionAsPercentageOfParticipantsEligibleCompensation
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The minimum percentages that return should exceed growth in consumer price index annually. + References No definition available. + Details
Name: | mtg_MinimumPercentageReturnShouldExceedGrowthInConsumerPriceIndexAnnually
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents minimum percentages of gain loss consider for amortization. + References No definition available. + Details
Name: | mtg_MinimumPercentagesOfGainLossConsiderForAmortization
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The investment in international mutual funds primarily based in Europe and the Pacific Basin, as a percentage of the equity investments range. + References No definition available. + Details
Name: | mtg_PercentofinternationalmutualfundsequityallocationincompaniesprimarilybasedinEuropeandPacificBasin
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The investment in international mutual funds (emerging markets), as a percentage of the equity investments range. + References No definition available. + Details
Name: | mtg_Percentofinternationalmutualfundsequityallocationinemergingmarkets
Namespace Prefix: | mtg_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e2709-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 5: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 18 -URI https://asc.fasb.org/extlink&oid=123450688&loc=d3e4587-114921 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI https://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanContributionsByEmployer
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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_DefinedBenefitPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix: | us-gaap_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPensionPlansPostretirementOrSupplementalPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |