XML 55 R37.htm IDEA: XBRL DOCUMENT v3.21.1

Reinsurance - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Effects of Reinsurance [Line Items]
Reinsurance recoverable on loss reserves	$ 102,901	$ 25,756	$ 95,042	$ 21,641
Ceded premiums	$ 43,637	31,576
Quota Share Reinsurance Agreements
Effects of Reinsurance [Line Items]
Ceding commission, percentage (as a percent)	20.00%
Reinsurance, Quota Share Reinsurance Agreement, Terms, Annual Loss Ratio Cap	300.00%
Reinsurance, Quota Share Reinsurance Agreement, Terms, Lifetime Loss Ratio Cap	200.00%
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)	90.00%
Reinsurance recoverable on loss reserves	$ 102,900		$ 95,000
Credit Union QSR
Effects of Reinsurance [Line Items]
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)	80.00%
Excess of Loss Reinsurance Agreement, Home Re
Effects of Reinsurance [Line Items]
Ceded premiums	$ 10,300	$ 4,700
Excess of Loss Reinsurance Agreement, Home Re | Minimum
Effects of Reinsurance [Line Items]
Amortization period excess of loss reinsurance coverage	10 years
Excess of Loss Reinsurance Agreement, Home Re | Maximum
Effects of Reinsurance [Line Items]
Amortization period excess of loss reinsurance coverage	12 years 6 months
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 | Minimum
Effects of Reinsurance [Line Items]
Term of mortgage insurance-linked notes	10 years
Home Re special purpose insurers | Maximum
Effects of Reinsurance [Line Items]
Term of mortgage insurance-linked notes	12 years 6 months
Financial Asset Equal To Or Greater Than 60 Days Past Due | Excess of Loss Reinsurance Agreement, Home Re
Effects of Reinsurance [Line Items]
Percent of delinquent reinsured loans to total reinsured loans	4.00%

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

The percent of delinquent reinsured principal balance of loans to total reinsured principal balance of loans that causes a trigger event if exceeded.

+ References

No definition available.

+ Details

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

X

- Definition

Reinsurance, Quota Share Reinsurance Agreement, Terms, Annual Loss Ratio Cap

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsAnnualLossRatioCap
Namespace Prefix:	mtg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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, Lifetime Loss Ratio Cap

+ References

No definition available.

+ Details

Name:	mtg_ReinsuranceQuotaShareReinsuranceAgreementTermsLifetimeLossRatioCap
Namespace Prefix:	mtg_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

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, 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

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

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

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_QuotaShareReinsuranceAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_ReinsurancePolicyTypeAxis=mtg_CreditUnionQuotaShareReinsuranceAgreementMember
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:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	srt_RangeAxis=srt_MaximumMember
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_FinancingReceivablesPeriodPastDueAxis=mtg_FinancialAssetEqualToOrGreaterThan60DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: