Statutory capital (Details) (USD $)	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
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)	10Y
Percentage of net premiums earned that incurred losses must exceed to enable early withdrawals from contingency loss reserves (in hundredths)	35.00%
Net (loss) Income	$ (436,277,000)	$ 113,651,000	$ (44,669,000)
Surplus	1,657,349,000	1,692,392,000	1,442,407,000
Contingency Reserve	4,104,000	5,480,000	417,587,000
Statutory capital requirements [Abstract]
Maximum permitted risk-to-capital ratio	25 to 1
Amount by which the company exceeded minimum policyholders position on a combined basis	249,000,000
Risk-to-capital ratio on a combined basis at end of period	22.2 to 1
Mortgage Guaranty Insurance Corporation [Member]
Related Party Transaction [Line Items]
Surplus contributions made to subsidiary by the parent company	200,000,000	200,000,000	0
Dividends paid by MGIC to the parent company	0	0	0
Statutory capital requirements [Abstract]
Amount by which MGIC exceeded minimum policyholders position	185,000,000
MGIC's risk-to-capital ratio at end of period	20.3 to 1
Other insurance subsidiaries [Member]
Related Party Transaction [Line Items]
Surplus contributions made to subsidiary by the parent company	$ 0	$ 0	$ 0