Loss Reserves - Reconciliation of Beginning and Ending Balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Loss Reserve [Roll Forward]
Reserve at beginning of period	$ 880,537	$ 555,334
Less reinsurance recoverable	95,042	21,641
Net reserve at beginning of period	785,495	533,693
Losses and LAE incurred in respect of delinquency notices received in:
Current year	95,534	301,699
Prior years	(5,968)	17,317
Total losses incurred	89,566	319,016
Losses and LAE paid in respect of delinquency notices received in:
Current year	339	1,486
Prior years	48,842	93,937
Reinsurance terminations	0	(20)
Total losses paid	49,181	95,403
Net reserve at end of period	825,880	757,306
Plus reinsurance recoverables	107,029	83,143
Reserve at end of period	$ 932,909	$ 840,449