Loss Reserves (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan	Mar. 31, 2017 USD ($) loan
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of prior year delinquent inventory resolved (as a percent)	31.00%		29.00%
Prior years | $	$ 81,983		$ 127,224
Premium refund liability, expected claim payments | $	56,000	$ 61,000
Prior years | $	$ (35,220)		$ (52,797)
Default notices for loans in IADAs (in loans)		9,294
Primary Delinquent Inventory [Roll Forward]
Delinquent inventory at the beginning of period (in loans)	46,556		50,282
New notices (in loans)	14,623		14,939
Cures (in loans)	(18,073)		(17,128)
Paids (including those charged to a deductible or captive) (in loans)	(1,571)		(2,635)
Rescissions and denials (in loans)	(68)		(95)
Other items removed from inventory (in loans)	(224)		(14)
Delinquent inventory at end of period (in loans)	41,243	46,556	45,349
Settlements for commutations of coverage, pools of nonperforming loans
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years | $	$ 7,000
Decrease in estimated claim rate on primary defaults
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years | $	(47,000)		$ (54,000)
Increase in estimated severity on primary defaults
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years | $	16,000		4,000
Change in estimates related to pool reserves, LAE reserves and reinsurance
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years | $	$ (4,000)		$ (3,000)