Fair Value Measurements, Unobservable Input Reconciliation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as net impairment losses recognized in earnings	$ 144	$ 328	$ 2,310
State premium tax credit investments, average maturity	5 years
Annual average discount rate (in hundredths)	7.30%mtg_FairValueAnnualAverageDiscountRate
Obligations of U.S. States and Political Subdivisions [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	2,423	3,130	114,226
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as realized investment gains (losses), net		0	(8,669)
Included in earnings and reported as net impairment losses recognized in earnings			0
Included in earnings and reported as losses incurred, net	0	0	0
Included in other comprehensive income			5,630
Purchases	30	30	27
Sales	(607)	(737)	(108,084)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Balance at end of period	1,846	2,423	3,130
Amount of total losses included in earnings for the period attributable to the change in unrealized losses on assets still held at period end	0	0	0
Corporate Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	0	17,114	60,228
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as realized investment gains (losses), net		(225)	(3,129)
Included in earnings and reported as net impairment losses recognized in earnings			(2,310)
Included in earnings and reported as losses incurred, net	0	0	0
Included in other comprehensive income			733
Purchases	0	0	0
Sales	0	(16,889)	(38,408)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Balance at end of period	0	0	17,114
Amount of total losses included in earnings for the period attributable to the change in unrealized losses on assets still held at period end	0	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	321	321	321
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as realized investment gains (losses), net		0	0
Included in earnings and reported as net impairment losses recognized in earnings			0
Included in earnings and reported as losses incurred, net	0	0	0
Included in other comprehensive income			0
Purchases	0	0	0
Sales	0	0	0
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Balance at end of period	321	321	321
Amount of total losses included in earnings for the period attributable to the change in unrealized losses on assets still held at period end	0	0	0
Total Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	2,744	20,565	174,775
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as realized investment gains (losses), net		(225)	(11,798)
Included in earnings and reported as net impairment losses recognized in earnings			(2,310)
Included in earnings and reported as losses incurred, net	0	0	0
Included in other comprehensive income			6,363
Purchases	30	30	27
Sales	(607)	(17,626)	(146,492)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Balance at end of period	2,167	2,744	20,565
Amount of total losses included in earnings for the period attributable to the change in unrealized losses on assets still held at period end	0	0	0
Real Estate Acquired [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	13,280	3,463	1,621
Total realized/unrealized gains (losses) [Abstract]
Included in earnings and reported as realized investment gains (losses), net		0	0
Included in earnings and reported as net impairment losses recognized in earnings			0
Included in earnings and reported as losses incurred, net	(4,129)	(4,959)	(1,126)
Included in other comprehensive income			0
Purchases	42,247	39,188	11,991
Sales	(38,740)	(24,412)	(9,023)
Transfers into Level 3	0	0	0
Transfers out of Level 3	0	0	0
Balance at end of period	12,658	13,280	3,463
Amount of total losses included in earnings for the period attributable to the change in unrealized losses on assets still held at period end	$ 0	$ 0	$ 0

This element represents annual average discount rate used for fair value of state premium tax credit investments.

No definition available.

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- Definition

This element represents total gains or losses for the period reported as realized investment losses, net, arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value.

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No definition available.

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This element represents total losses for the period (realized and unrealized), arising from assets measured at fair value on a recurring basis using unobservable inputs (Level 3), which are included in earnings or resulted in a change in net asset value and are attributable to the change in unrealized losses on assets still held at the end of the period.

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This element represents state premium tax credit investments, average maturity.

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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.

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Amount of gain (loss) recognized in other comprehensive income (loss) 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.

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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.

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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.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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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.

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The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

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