Reinsurance - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Effects of Reinsurance [Line Items]
Reinsurance recoverable on loss reserves		$ 107,029	$ 83,143	$ 107,029	$ 83,143	$ 95,042	$ 21,641
Ceded premiums		$ 35,039	47,173	$ 122,664	144,489
Home Re special purpose insurers
Effects of Reinsurance [Line Items]
Percent of total trust assets invested in cash or direct U.S. federal government obligations				99.50%
Quota Share Reinsurance Agreements
Effects of Reinsurance [Line Items]
Ceding commission, percentage (as a percent)				20.00%
Reinsurance, Quota Share Reinsurance Agreement, Terms, Annual Loss Ratio Cap		300.00%		300.00%
Reinsurance, Quota Share Reinsurance Agreement, Terms, Lifetime Loss Ratio Cap		200.00%		200.00%
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)				90.00%
Reinsurance recoverable on loss reserves		$ 107,000		$ 107,000		$ 95,000
Quota Share Reinsurance Agreements | Subsequent Event
Effects of Reinsurance [Line Items]
Contingent termination fee	$ 5,000
Credit Union QSR
Effects of Reinsurance [Line Items]
Threshold for private mortgage insurer eligibility requirements for termination election (less than) (as a percent)				80.00%
Excess of Loss Reinsurance Agreement, Home Re
Effects of Reinsurance [Line Items]
Ceded premiums		$ 12,100	$ 3,700	$ 32,400	$ 12,800
Excess of Loss Reinsurance Agreement, Home Re | Minimum
Effects of Reinsurance [Line Items]
Amortization period excess of loss reinsurance coverage				10 years
Excess of Loss Reinsurance Agreement, Home Re | Maximum
Effects of Reinsurance [Line Items]
Amortization period excess of loss reinsurance coverage				12 years 6 months
Excess of Loss Reinsurance Agreement, Home Re | Financial Asset Equal To Or Greater Than 60 Days Past Due
Effects of Reinsurance [Line Items]
Percent of delinquent reinsured loans to total reinsured loans				4.00%