Loss Reserves (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2016 loan	Sep. 30, 2017 USD ($) loan	Sep. 30, 2016 loan	Sep. 30, 2017 USD ($) loan	Sep. 30, 2016 USD ($) loan	Dec. 31, 2016 USD ($)
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Other items removed from inventory (in loans) | loan		(209)	0	(1,337)	(1,273)
Prior years | $				$ 407,977	$ 549,706
Premium refund liability, expected claim payments | $		$ 68,000		68,000		$ 85,000
Prior years | $				$ (134,780)	$ (99,591)
Primary Default Inventory [Roll Forward]
Default inventory at the beginning of period (in loans) | loan	51,433	41,317	52,558	50,282	62,633
New notices (in loans) | loan	5,519	15,950	17,607	45,352	50,418
Cures (in loans) | loan		(13,546)	(15,556)	(45,382)	(50,249)
Paids (including those charged to a deductible or captive) (in loans) | loan		(2,195)	(3,051)	(7,403)	(9,619)
Rescissions and denials (in loans) | loan		(82)	(125)	(277)	(477)
Other items removed from inventory (in loans) | loan		(209)	0	(1,337)	(1,273)
Default inventory at end of period (in loans) | loan		41,235	51,433	41,235	51,433
Decrease in estimated claim rate on primary defaults
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Percentage of prior year default inventory resolved (as a percent)				59.00%	54.00%
Prior years | $				$ (138,000)	$ (108,000)
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 | $				54,000
Settlements for commutations of coverage, pools of nonperforming loans, and claims paying practiices
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years | $					52,000
(Decrease) increase in estimated severity on primary defaults
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Prior years | $				(2,000)	12,000
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 | $				$ 5,000	$ (4,000)