Reserve for Losses and Loss Adjustment Expenses - Narrative (Details) $ in Thousands	3 Months Ended	6 Months Ended	12 Months Ended
	Dec. 31, 2018 USD ($) loan	Sep. 30, 2020	Dec. 31, 2020 USD ($) loan	Dec. 31, 2019 USD ($) loan	Dec. 31, 2018 USD ($) loan	Dec. 31, 2017 USD ($) loan
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred claims and claim adjustment expenses			$ 13,686	$ 11,871	$ 7,651
Favorable prior year development			16,223	17,576	$ 24,863
Reserve for losses and LAE, for prior years			$ 39,400	$ 20,000
Loans in default at end of year | loan	4,024		31,469	5,947	4,024
Reserve for losses and LAE	$ 49,464		$ 374,941	$ 69,362	$ 49,464	$ 46,850
Hurricane
Liability for Claims and Claims Adjustment Expense [Line Items]
Reserve for losses and LAE						$ 11,100
Number of loans in hurricane impacted areas in default | loan	2,288				2,288	2,288
Number of loans in hurricane impacted areas cured | loan					2,150
Reduction of reserves on hurricane-related defaults	$ 9,900
COVID-19
Liability for Claims and Claims Adjustment Expense [Line Items]
Loans in default at end of year | loan			28,922
Reserve rate		7.00%
Reserve for losses and LAE			$ 316,300
Percent change used in calculation of expense			1.00%
Effect of percentage point decrease on liability claim and claim expense adjustment expense			$ 35,000