XML 40 R61.htm IDEA: XBRL DOCUMENT
v3.19.3.a.u2

Reinsurance - Narrative (Details) - USD ($) | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Jun. 30, 2019 | Dec. 31, 2019 | Jun. 30, 2019 | Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Reinsurance recoverable on loss reserves |  | $ 21,641,000 |  |  |  | $ 21,641,000 | $ 33,328,000 | $ 48,474,000 | $ 50,493,000
Ceded premiums earned |  |  |  |  |  | 129,337,000 | 111,391,000 | $ 125,735,000 |
Quota Share Reinsurance Agreement, 2019 |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Contingent termination fee |  |  |  |  |  | $ 0 |  |  |
Threshold for private mortgage insurer eligibility requirements for termination election |  |  |  |  |  | 90.00% |  |  |
Quota share, percentage |  |  |  |  |  | 30.00% |  |  |
Cede rate, option 1 |  |  |  |  |  | 25.00% |  |  |
Cede rate, option 2 |  |  |  |  |  | 20.00% |  |  |
Ceding commission, percentage |  |  |  |  |  | 20.00% |  |  |
Loss ratio |  |  |  |  |  | 62.00% |  |  |
Quota Share Reinsurance Agreement, 2018 |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Contingent termination fee |  |  |  |  |  | $ 0 |  |  |
Threshold for private mortgage insurer eligibility requirements for termination election |  |  |  |  |  | 90.00% |  |  |
Quota share, percentage |  |  |  |  |  | 30.00% |  |  |
Ceding commission, percentage |  |  |  |  |  | 20.00% |  |  |
Loss ratio |  |  |  |  |  | 62.00% |  |  |
Quota Share Reinsurance Agreement, 2017 |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Contingent termination fee |  |  |  |  |  | $ 0 |  |  |
Threshold for private mortgage insurer eligibility requirements for termination election |  |  |  |  |  | 90.00% |  |  |
Quota share, percentage |  |  |  |  |  | 30.00% |  |  |
Ceding commission, percentage |  |  |  |  |  | 20.00% |  |  |
Loss ratio |  |  |  |  |  | 60.00% |  |  |
Quota Share Reinsurance Agreement, 2015 |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Contingent termination fee | $ 6,800,000 | $ 0 |  |  |  |  |  |  |
Threshold for private mortgage insurer eligibility requirements for termination election |  |  |  |  |  | 90.00% |  |  |
Quota share, percentage |  | 15.00% | 30.00% |  |  |  |  |  |
Loss ratio |  |  |  |  |  | 68.00% |  |  |
Quota Share Reinsurance Agreements, Excluding Captives |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Reinsurance recoverable on loss reserves |  | $ 21,600,000 |  |  |  | $ 21,600,000 | 33,200,000 |  |
Quota Share Reinsurance Agreement, 2020 | Forecast |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Contingent termination fee |  |  |  |  | $ 0 |  |  |  |
Threshold for private mortgage insurer eligibility requirements for termination election |  |  |  |  | 90.00% |  |  |  |
Quota share, percentage |  |  |  |  | 30.00% |  |  |  |
Cede rate, option 1 |  |  |  |  | 25.00% |  |  |  |
Cede rate, option 2 |  |  |  |  | 20.00% |  |  |  |
Loss ratio |  |  |  |  | 62.00% |  |  |  |
Quota Share Reinsurance Agreement, 2021 | Forecast |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Contingent termination fee |  |  |  | $ 0 |  |  |  |  |
Threshold for private mortgage insurer eligibility requirements for termination election |  |  |  | 90.00% |  |  |  |  |
Quota share, percentage |  |  |  | 17.50% |  |  |  |  |
Cede rate, option 1 |  |  |  | 14.50% |  |  |  |  |
Cede rate, option 2 |  |  |  | 12.00% |  |  |  |  |
Loss ratio |  |  |  | 62.00% |  |  |  |  |
Excess of Loss Reinsurance Agreements, Home Re Entities |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Amortization period excess of loss reinsurance coverage |  |  |  |  |  | 10 years |  |  |
Ceded premiums earned |  |  |  |  |  | $ 17,600,000 | $ 2,800,000 |  |
Home Re special purpose insurers |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Percent of total trust assets invested in cash or direct U.S. federal government obligations |  |  |  |  |  | 99.50% |  |  |
Home Re special purpose insurers | Mortgage Insurance Linked Notes |  |  |  |  |  |  |  |  |
Effects of Reinsurance [Line Items] |  |  |  |  |  |  |  |  |
Term of mortgage insurance-linked notes |  |  |  |  |  | 10 years |  |  |

X
- Definition Amortization Period Excess of Loss Reinsurance Coverage + References No definition available. + Details
Name: | mtg_AmortizationPeriodExcessofLossReinsuranceCoverage
Namespace Prefix: | mtg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reinsurance, Quota Share Reinsurance Agreement, Terms, Ceding Commission, Percent + References No definition available. + Details
Name: | mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsCedingCommissionPercent
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reinsurance, Quota Share Reinsurance Agreement, Terms, Ceding Rate, Percent, Option One + References No definition available. + Details
Name: | mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsCedingRatePercentOptionOne
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reinsurance, Quota Share Reinsurance Agreement, Terms, Ceding Rate, Percent, Option Two + References No definition available. + Details
Name: | mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsCedingRatePercentOptionTwo
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reinsurance, Quota Share Reinsurance Agreement, Terms, Contingent Termination Fee + References No definition available. + Details
Name: | mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsContingentTerminationFee
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Reinsurance, Quota Share Reinsurance Agreement, Terms, Quota Share, Percent + References No definition available. + Details
Name: | mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsQuotaSharePercent
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reinsurance, Quota Share Reinsurance Agreement, Terms, Threshold For Private Mortgage Insurer Eligibility Requirements For Termination Election + References No definition available. + Details
Name: | mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsThresholdForPrivateMortgageInsurerEligibilityRequirementsForTerminationElection
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Reinsurance Retention Policy, Percent Of Total Trust Assets Invested In Cash Or Direct U.S. Federal Government Obligations + References No definition available. + Details
Name: | mtg_ReinsuranceRetentionPolicyPercentOfTotalTrustAssetsInvestedInCashOrDirectU.S.FederalGovernmentObligations
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of earned premiums ceded to other entities. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17(Column C)) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(1)) -URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=84167274&loc=d3e27175-158546 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 605 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547 + Details
Name: | us-gaap_CededPremiumsEarned
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
Name: | us-gaap_DebtInstrumentTerm
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
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_EffectsOfReinsuranceLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Ratio of non-life losses and loss expenses to non-life net premiums earned. + References No definition available. + Details
Name: | us-gaap_LossRatio
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount, after valuation allowance, recoverable under reinsurance contracts for losses reported to the ceding insurer but not yet paid and amounts expected for incurred losses and settlement expenses, which have not yet been reported to the ceding insurer. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=99404803&loc=d3e21412-158489 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 20 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=99397103&loc=d3e6824-158387 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
Name: | us-gaap_ReinsuranceRecoverableForUnpaidClaimsAndClaimsAdjustments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreement2019Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreement2018Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreement2017Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreement2015Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreementsExcludingCaptivesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreement2020Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementScenarioAxis=srt_ScenarioForecastMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsurancePolicyTypeAxis=mtg_QuotaShareReinsuranceAgreement2021Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ReinsurancePolicyTypeAxis=mtg_ExcessofLossReinsuranceAgreementsHomeReEntitiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=mtg_HomeRespecialpurposeinsurersMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DebtInstrumentAxis=mtg_MortgageInsuranceLinkedNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |