XML 63 R48.htm IDEA: XBRL DOCUMENT
v3.5.0.2

Loss Reserves (Details) $ in Thousands | 3 Months Ended | 9 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Sep. 30, 2016 USD ($) loan | Sep. 30, 2015 USD ($) loan | Sep. 30, 2016 USD ($) loan | Sep. 30, 2015 USD ($) loan | Sep. 30, 2016 USD ($) loan | Dec. 31, 2015 USD ($) loan | Sep. 30, 2015 loan
Loss Reserve [Roll Forward] |  |  |  |  |  |  |
Reserve at beginning of period |  |  | $ 1,893,402 | $ 2,396,807 |  |  |
Less reinsurance recoverable |  |  | 44,487 | 57,841 |  |  |
Net reserve at beginning of period |  |  | 1,848,915 | 2,338,966 |  |  |
Losses and LAE incurred in respect of defaults related to: |  |  |  |  |  |  |
Current year |  |  | 292,090 | 338,611 |  |  |
Prior years |  |  | (99,591) | (90,130) |  |  |
Subtotal |  |  | 192,499 | 248,481 |  |  |
Losses and LAE paid in respect of defaults related to: |  |  |  |  |  |  |
Current year |  |  | 5,942 | 9,227 |  |  |
Prior years |  |  | 549,706 | 652,465 |  |  |
Reinsurance terminations |  |  | (2,854) | (15,440) |  |  |
Subtotal |  |  | 552,794 | 646,252 |  |  |
Net reserve at end of period | $ 1,488,620 | $ 1,941,195 | 1,488,620 | 1,941,195 |  |  |
Plus reinsurance recoverables | 46,863 | 38,748 | 46,863 | 38,748 |  |  |
Reserve at end of period | $ 1,535,483 | $ 1,979,943 | 1,535,483 | 1,979,943 |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Prior years |  |  | (99,591) | (90,130) |  |  |
Prior years |  |  | $ 549,706 | $ 652,465 |  |  |
Premium refund liability, expected claim payments |  |  |  |  | $ 91,000 | $ 102,000 |
Pool insurance notice inventory [Abstract] |  |  |  |  |  |  |
Historical average period for uncured default to develop into paid claim |  |  | 12 months |  |  |  |
Primary Default Inventory [Roll Forward] |  |  |  |  |  |  |
Default inventory at the beginning of period | loan | 52,558 | 66,357 | 62,633 | 79,901 |  |  |
New notices | loan | 17,607 | 19,509 | 50,418 | 55,856 |  |  |
Cures | loan | (15,556) | (17,036) | (50,249) | (56,700) |  |  |
Paids (including those charged to a deductible or captive) | loan | (3,051) | (3,958) | (9,619) | (12,671) |  |  |
Rescissions and denials | loan | (125) | (230) | (477) | (623) |  |  |
Other items removed from inventory | loan | 0 | 0 | (1,273) | (1,121) |  |  |
Default inventory at end of period | loan | 51,433 | 64,642 | 51,433 | 64,642 |  |  |
Default inventory, measurement period threshold (in months) |  |  | 12 months |  |  |  |
Aging of the Primary Default Inventory [Abstract] |  |  |  |  |  |  |
3 months or less | loan |  |  |  |  | 12,333 | 13,053 | 13,991
3 months or less (in hundredths) |  |  |  |  | 24.00% | 21.00% | 22.00%
4 - 11 months | loan |  |  |  |  | 12,648 | 15,763 | 14,703
4 - 11 months (in hundredths) |  |  |  |  | 25.00% | 25.00% | 23.00%
12 months or more | loan |  |  |  |  | 26,452 | 33,817 | 35,948
12 months or more (in hundredths) |  |  |  |  | 51.00% | 54.00% | 55.00%
Total primary default inventory | loan | 52,558 | 66,357 | 62,633 | 79,901 | 51,433 | 62,633 | 64,642
Total primary default inventory (in hundredths) |  |  |  |  | 100.00% | 100.00% | 100.00%
Primary claims received inventory included in ending default inventory | loan |  |  |  |  | 1,636 | 2,769 | 2,982
Primary claims received inventory included in ending default inventory (in hundredths) |  |  |  |  | 3.00% | 4.00% | 5.00%
Percent of default inventory in default for more than 36 months |  |  |  |  | 48.00% | 50.00% | 50.00%
Number of payments delinquent [Abstract] |  |  |  |  |  |  |
3 payments or less | loan |  |  |  |  | 18,374 | 20,360 | 20,637
3 payments or less (in hundredths) |  |  |  |  | 36.00% | 33.00% | 32.00%
4 - 11 payments | loan |  |  |  |  | 12,282 | 15,092 | 14,890
4 - 11 payments (in hundredths) |  |  |  |  | 24.00% | 24.00% | 23.00%
12 payments or more | loan |  |  |  |  | 20,777 | 27,181 | 29,115
12 payments or more (in hundredths) |  |  |  |  | 40.00% | 43.00% | 45.00%
Total primary default inventory | loan | 52,558 | 66,357 | 62,633 | 79,901 | 51,433 | 62,633 | 64,642
Total primary default inventory (in hundredths) |  |  |  |  | 100.00% | 100.00% | 100.00%
Pool insurance notice inventory (in number of loans) | loan |  |  |  |  | 1,979 | 2,739 | 2,950
Premium refund liability, expected future rescissions |  |  |  |  | $ 6,000 | $ 7,000 |
Decrease in estimated claim rate on primary defaults |  |  |  |  |  |  |
Losses and LAE incurred in respect of defaults related to: |  |  |  |  |  |  |
Prior years |  |  | $ (108,000) | $ (95,000) |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Prior years |  |  | $ (108,000) | $ (95,000) |  |  |
Percentage of prior year default inventory resolved (in hundredths) |  |  | 54.00% | 52.00% |  |  |
Increase in estimated severity on primary defaults |  |  |  |  |  |  |
Losses and LAE incurred in respect of defaults related to: |  |  |  |  |  |  |
Prior years |  |  | $ 12,000 | $ 12,000 |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Prior years |  |  | 12,000 | 12,000 |  |  |
Change in estimates related to pool reserves, LAE reserves and reinsurance |  |  |  |  |  |  |
Losses and LAE incurred in respect of defaults related to: |  |  |  |  |  |  |
Prior years |  |  | (4,000) | (7,000) |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Prior years |  |  | (4,000) | (7,000) |  |  |
Change in estimates related to disputes on claims paying practices and IBNR |  |  |  |  |  |  |
Losses and LAE incurred in respect of defaults related to: |  |  |  |  |  |  |
Prior years |  |  |  | 21,000 |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Prior years |  |  |  | $ 21,000 |  |  |
Settlements For Claims Paying Practices And Nonperforming Loan Sale |  |  |  |  |  |  |
Losses and LAE paid in respect of defaults related to: |  |  |  |  |  |  |
Prior years |  |  | 52,000 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Prior years |  |  | $ 52,000 |  |  |  |

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

X
- Definition The average period, on a historical basis, for a default which is not cured to develop into a paid claim. + References No definition available. + Details
Name: | mtg_HistoricalAveragePeriodForUncuredDefaultToDevelopIntoPaidClaim
Namespace Prefix: | mtg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Loss Reserve, Default Inventory Measurement Period Threshold + References No definition available. + Details
Name: | mtg_LossReserveDefaultInventoryMeasurementPeriodThreshold
Namespace Prefix: | mtg_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | mtg_LossReserveRollForward
Namespace Prefix: | mtg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of loans in the primary default inventory that have been delinquent for twelve payments or more. + References No definition available. + Details
Name: | mtg_NumberOfPaymentsDelinquent12PaymentsOrMore
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of loans in the primary default inventory that have been delinquent for twelve payments or more. + References No definition available. + Details
Name: | mtg_NumberOfPaymentsDelinquent12PaymentsOrMorePercentage
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of loans in the primary default inventory that have been delinquent for three payments or less. + References No definition available. + Details
Name: | mtg_NumberOfPaymentsDelinquent3PaymentsOrLess
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of loans in the primary default inventory that have been delinquent for three payments or less. + References No definition available. + Details
Name: | mtg_NumberOfPaymentsDelinquent3PaymentsOrLessPercentage
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of loans in the primary default inventory that have been delinquent for at least four payments but no more than eleven payments. + References No definition available. + Details
Name: | mtg_NumberOfPaymentsDelinquent4To11Payments
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of loans in the primary default inventory that have been delinquent for at least four payments but no more than eleven payments. + References No definition available. + Details
Name: | mtg_NumberOfPaymentsDelinquent4To11PaymentsPercentage
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition The percentage of the prior year default inventory resolved, which is used in the calculation of the change in the severity and claim rates. + References No definition available. + Details
Name: | mtg_PercentageOfPriorYearDefaultInventoryResolved
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of loans included in the pool insurance notice inventory as of the end of the reporting period. + References No definition available. + Details
Name: | mtg_PoolInsuranceNoticeInventory
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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

X
- Definition The carrying amount for the estimate of premiums to be refunded on expected claim payments. + References No definition available. + Details
Name: | mtg_PremiumRefundLiabilityExpectedClaimPayments
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The carrying amount for the estimate of premiums to be refunded on expected future rescissions. + References No definition available. + Details
Name: | mtg_PremiumRefundLiabilityExpectedFutureRescissions
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition The number of loans in the primary default inventory. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventory
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of loans in the primary default inventory that are in the claims received inventory. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryClaimsReceivedInventory
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of loans in the primary default inventory that are in the claims received inventory. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryClaimsReceivedInventoryPercentage
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Deductions from the primary default inventory resulting from loans in default being brought current. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryCures
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of loans that have been in the primary default inventory for at least four months but no greater than eleven months as of the balance sheet date. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryFourToElevenMonths
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of loans that have been in the primary default inventory for at least four months but no greater than eleven months as of the balance sheet date. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryFourToElevenMonthsPercentage
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Additions to the primary default inventory resulting from new notices of defaulted loans. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryNewNotices
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Other deductions from the primary default inventory, including items removed for settlements + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryOtherItemsRemoved
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Deductions from the primary default inventory resulting from claims being paid, including those charged to a deductible or captive. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryPaids
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage of loans in the primary default inventory. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryPercentage
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Deductions from the primary default inventory resulting from rescissions and denials. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryRescissionsAndDenials
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryRollForward
Namespace Prefix: | mtg_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of loans that have been in the primary default inventory for three months or less as of the balance sheet date. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryThreeMonthsOrLess
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of loans that have been in the primary default inventory for three months or less as of the balance sheet date. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryThreeMonthsOrLessPercentage
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of loans that have been in the primary default inventory for twelve months or more as of the balance sheet date. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryTwelveMonthsOrMore
Namespace Prefix: | mtg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Primary Default Inventory Twelve Months Or More, Percent Of Primary Default Inventory In Default For Twelve Months Or More In Default For More Than Thirty Six Consecutive Months + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryTwelveMonthsOrMorePercentOfPrimaryDefaultInventoryInDefaultForTwelveMonthsOrMoreInDefaultForMoreThanThirtySixConsecutiveMonths
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The percentage of loans that have been in the primary default inventory for twelve months or more as of the balance sheet date. + References No definition available. + Details
Name: | mtg_PrimaryDefaultInventoryTwelveMonthsOrMorePercentage
Namespace Prefix: | mtg_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Decrease in losses paid resulting from cancellations of reinsurance agreements, with no future premium ceded and funds for any incurred but unpaid losses transferred to the entity. + References No definition available. + Details
Name: | mtg_ReinsuranceTerminations
Namespace Prefix: | mtg_
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_CausesOfIncreaseDecreaseInLiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The amount needed to reflect the estimated ultimate cost of settling claims relating to insured events that have occurred on or before the balance sheet date, whether or not reported to the insurer at that date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a),(b),(c) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- References No definition available. + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of payments to settle claims incurred in the current period and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidCurrentYear1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of payments to settle claims incurred in prior periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseClaimsPaidPriorYears1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of expense for claims incurred and costs incurred in the claim settlement process. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaims1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseIncurredClaimsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Liability as of the balance sheet date for amounts representing estimated cost of settling unpaid claims under the terms of the underlying insurance policies, less estimated reinsurance recoveries on such claims. This includes an estimate for claims which have been incurred but not reported. Claim adjustment expenses represent the costs estimated to be incurred in the settlement of unpaid claims. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6482485&loc=d3e14764-158437 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 13 -Subparagraph a -Article 7 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Financial Reporting Release (FRR) -Number 403 -Paragraph 04 -Subparagraph b + Details
Name: | us-gaap_LiabilityForUnpaidClaimsAndClaimsAdjustmentExpenseNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of payments to settle insured claims and pay costs incurred in the claims settlement process. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3536-108585 + Details
Name: | us-gaap_PaymentsForLossesAndLossAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount after valuation allowance of reinsurance recoverables for losses reported to the ceding insurer but not yet paid, amounts expected of incurred losses and settlement expenses, which have not yet been reported to the ceding insurer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 310 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6485522&loc=d3e21412-158489 + Details
Name: | us-gaap_ReinsuranceRecoverablesOnUnpaidLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of expense for claims incurred in the current reporting period and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersCurrentYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of expense (reversal of expense) for claims incurred in prior reporting periods and related claims settlement costs. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 235 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-18) -URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e575016-122915 + Details
Name: | us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_NoncatastrophicEventAxis=mtg_IncreaseDecreaseInExpectedClaimRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncatastrophicEventAxis=mtg_IncreaseDecreaseInEstimatedSeverityPrimaryDefaultsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncatastrophicEventAxis=mtg_IncreaseDecreaseRelatedToPoolReservesLaeReservesAndReinsuranceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncatastrophicEventAxis=mtg_ChangeInReserveEstimatesRelatedToDisputesOnClaimsPayingPracticesAndIBNRMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_NoncatastrophicEventAxis=mtg_SettlementsForClaimsPayingPracticesAndNonperformingLoanSaleMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |