Loss Reserves (Details) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan	Jun. 30, 2017 loan	Jun. 30, 2018 USD ($) loan	Jun. 30, 2017 USD ($) 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)				51.00%	48.00%
Prior years | $				$ 173,313	$ 298,847
Premium refund liability, expected claim payments | $	$ 50,000	$ 61,000		50,000
Prior years | $				$ (97,966)	$ (103,948)
Default notices for loans in IADAs (in loans)		9,294
Primary Delinquent Inventory [Roll Forward]
Delinquent inventory at the beginning of period (in loans)	41,243		45,349	46,556	50,282
New notices (in loans)	12,159		14,463	26,782	29,402
Cures (in loans)	(15,350)		(14,708)	(33,423)	(31,836)
Paids (including those charged to a deductible or captive) (in loans)	(1,501)		(2,573)	(3,072)	(5,208)
Rescissions and denials (in loans)	(76)		(100)	(144)	(195)
Other items removed from inventory (in loans)	(438)		(1,114)	(662)	(1,128)
Delinquent inventory at end of period (in loans)	36,037	46,556	41,317	36,037	41,317
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 | $				$ 21,000	$ 45,000
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 | $				(120,000)	(104,000)
Increase in estimated severity on primary defaults
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years | $				19,000	2,000
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 | $				$ 3,000	$ (2,000)