Loss Reserves - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) loan Payment	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Loss reserves	$ 325,203	$ (118,685)	$ (311,616)
Minimum number of payments past due to be in default | Payment	2
Premium refund liability, expected claim payments	$ 30,000	$ 30,000
Percentage of prior year default inventory resolved (in hundredths)		69.00%	73.00%
Other items removed from inventory | loan	0	639	1,578
Losses for unpaid claims and adjustment expense	$ 109,923	$ 235,551	$ 327,743
Pool insurance notice inventory (in number of loans) | loan	680	653	859
Settlements for commutations of coverage, pools of nonperforming loans
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses for unpaid claims and adjustment expense		$ 30,000	$ 50,000
Settlements for claims paying practices
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Losses for unpaid claims and adjustment expense		$ 23,500
$1,000 Increase/Decrease In Average Severity Reserve Factor
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Loss reserves	$ 16,000
One Percentage Point Increase/Decrease In Average Claim Rate Reserve Factor
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Loss reserves	$ 34,000