Loss Reserves - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) loan	Dec. 31, 2015 USD ($) loan	Dec. 31, 2014 USD ($) loan
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses for unpaid claims and adjustment expense	$ 689,258	$ 823,058	$ 1,121,508
Other items removed from inventory | loan	1,273	1,121	193
Premium refund liability, expected claim payments	$ 85,000	$ 102,000
Percent of inventory in default for more than 36 consecutive months	47.00%	50.00%	53.00%
Pool insurance notice inventory (in number of loans) | loan	1,883	2,739	3,797
Premium refund liability, expected future rescissions	$ 5,000	$ 7,000
Payments for Settlements
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses for unpaid claims and adjustment expense	53,000	10,000
Payments for Settlements | Freddie Mac
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses for unpaid claims and adjustment expense	$ 42,000	$ 42,000	$ 42,000
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 (in hundredths)	63.00%	60.00%	58.00%