XML 79 R51.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Fair Value Measurements - Unobservable Input Reconciliation (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Total Investments |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |
Balance at beginning of period | $ 4,959 | $ 4,083 | $ 2,167
Total realized/unrealized gains (losses) [Abstract] |  |  |
Included in earnings and reported as net realized investment gains |  | 3,579 |
Included in earnings and reported as losses incurred, net | 0 | 0 | 0
Purchases | 0 | 4,258 | 2,541
Sales | (420) | (6,961) | (625)
Balance at end of period | 4,539 | 4,959 | 4,083
Total debt securities |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |
Balance at beginning of period | 691 | 1,228 | 1,846
Total realized/unrealized gains (losses) [Abstract] |  |  |
Included in earnings and reported as net realized investment gains |  | 0 |
Included in earnings and reported as losses incurred, net | 0 | 0 | 0
Purchases | 0 | 0 | 7
Sales | (420) | (537) | (625)
Balance at end of period | 271 | 691 | 1,228
Equity securities |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |
Balance at beginning of period | 4,268 | 2,855 | 321
Total realized/unrealized gains (losses) [Abstract] |  |  |
Included in earnings and reported as net realized investment gains |  | 3,579 |
Included in earnings and reported as losses incurred, net | 0 | 0 | 0
Purchases | 0 | 4,258 | 2,534
Sales | 0 | (6,424) | 0
Balance at end of period | 4,268 | 4,268 | 2,855
Real Estate Acquired |  |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward] |  |  |
Balance at beginning of period | 11,748 | 12,149 | 12,658
Total realized/unrealized gains (losses) [Abstract] |  |  |
Included in earnings and reported as net realized investment gains |  | 0 |
Included in earnings and reported as losses incurred, net | (1,315) | (1,142) | (2,322)
Purchases | 34,749 | 36,859 | 34,624
Sales | (32,469) | (36,118) | (32,811)
Balance at end of period | $ 12,713 | $ 11,748 | $ 12,149

X
- Definition Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included In Earnings, Reported As Net Realized Investment Gain, Net + References No definition available. + Details
Name: | mtg_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarningsReportedAsNetRealizedInvestmentGainNet
Namespace Prefix: | mtg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Definition Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSales
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258 + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_InvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByAssetClassAxis=mtg_RealEstateAcquiredMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |