XML 55 R39.htm IDEA: XBRL DOCUMENT
v3.20.1

Reinsurance - Variable Interest Entity (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2020 | Dec. 31, 2019
Home Re special purpose insurers |  |
Effects of Reinsurance [Line Items] |  |
Amortization period excess of loss reinsurance coverage | 10 years |
Term of mortgage insurance-linked notes | 10 years |
Remaining First Layer Retention | $ 352,625 | $ 353,415
Remaining Excess of Loss Reinsurance Coverages | $ 463,275 | 531,978
Percent of total trust assets invested in cash or direct U.S. federal government obligations | 99.50% |
Home Re 2018-1 |  |
Effects of Reinsurance [Line Items] |  |
Remaining First Layer Retention | $ 167,328 | 167,779
Remaining Excess of Loss Reinsurance Coverages | 233,626 | 260,957
Total VIE Assets | 245,314 | 269,451
Home Re 2019-1 |  |
Effects of Reinsurance [Line Items] |  |
Remaining First Layer Retention | 185,297 | 185,636
Remaining Excess of Loss Reinsurance Coverages | 229,649 | 271,021
Total VIE Assets | $ 247,276 | $ 283,150

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 Retention Policy, Debt Issued To Cover Insurance, Term + References No definition available. + Details
Name: | mtg_ReinsuranceRetentionPolicyDebtIssuedToCoverInsuranceTerm
Namespace Prefix: | mtg_
Data Type: | xbrli:durationItemType
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 Reinsurance Retention Policy, Remaining Excess of Loss Reinsurance Coverages + References No definition available. + Details
Name: | mtg_ReinsuranceRetentionPolicyRemainingExcessOfLossReinsuranceCoverages
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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 Stated amount that is the upper retention limit per entity policy. + References No definition available. + Details
Name: | us-gaap_ReinsuranceRetentionPolicyAmountRetained
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Carrying amount of the assets in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), where the reporting entity is not the VIE's primary beneficiary. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph a -URI http://asc.fasb.org/extlink&oid=118582676&loc=d3e5728-111685 + Details
Name: | us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssets
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Details
Name: | dei_LegalEntityAxis=mtg_HomeRe20181Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=mtg_HomeRe20191Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |