Statutory Capital (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Statutory Capital [Abstract]
Percentage of premiums earned required to be maintained as contingency loss reserves (in hundredths)	50.00%
Period that contingency loss reserves must be held (in years)	10 years
Percentage of net premiums earned that incurred losses must exceed to enable early withdrawals from contingency loss reserves (in hundredths)	35.00%
Percentage of surplus as regards policyholders (in hundredths)	10.00%
Statutory deferred tax assets admitted	$ 63,000,000
Net (loss) income	(902,878,000)	(436,277,000)	113,651,000
Surplus	748,592,000	1,657,349,000	1,692,392,000
Contingency Reserve	6,430,000	4,104,000	5,480,000
Statutory capital requirements [Abstract]
Amount of policyholders position above or below required MPP	640,000,000
Amount of required MPP	1,200,000,000
Risk-to-capital ratio on a combined basis at end of period	47.8 to 1
Mortgage Guaranty Insurance Corporation [Member]
Related Party Transaction [Line Items]
Surplus contributions made to subsidiary by the parent company	100,000,000	200,000,000	200,000,000
Dividends paid by MGIC to the parent company	0	0	0
Statutory capital requirements [Abstract]
Risk to capital ratio at end of period	44.7 to 1
Amount of policyholders position above or below required MPP	640,000,000
Amount of required MPP	1,200,000,000
Other Insurance Subsidiaries [Member]
Related Party Transaction [Line Items]
Surplus contributions made to subsidiary by the parent company	$ 0	$ 0	$ 0