SCHEDULE II - CONDENSED FINANCIAL INFORMATION OF REGISTRANT - SUPPLEMENTARY NOTES (Details) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 29, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Supplementary Insurance Information, by Segment [Line Items]
Percentage of statutory policyholders surplus used to determine maximum allowable dividends		10.00%
Convertible junior subordinated debentures		$ 256,872,000	$ 256,872,000
Other Insurance Subsidiaries
Supplementary Insurance Information, by Segment [Line Items]
Dividends paid to the parent company				$ 6,500,000
Distributions from other insurance subsidiaries to the parent company		0	52,001,000	38,500,000
Proceeds from contribution from parent		0		0
Parent Company
Supplementary Insurance Information, by Segment [Line Items]
Convertible junior subordinated debentures		$ 389,522,000	389,522,000
Mortgage Guaranty Insurance Corporation
Supplementary Insurance Information, by Segment [Line Items]
Adjusted statutory net income measurement period		3 years
Adjusted statutory net income dividend payment measurement period		2 years
Dividends paid to the parent company		$ 140,000,000	64,000,000	0
Additions to the surplus of MGIC from parent company funds		$ 0	$ 36,025,000	$ 0
Convertible Junior Subordinated Debentures, at 9% per annum, Due 2063
Supplementary Insurance Information, by Segment [Line Items]
Stated interest rate (in hundredths)		9.00%
Extinguishment of debt, amount	$ 132,700,000