Loss Reserves - Reconciliation of Beginning and Ending Balances (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 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	41,425	59,799
Prior years	(1,789)	1,157
Total losses incurred	39,636	60,956
Losses and LAE paid in respect of delinquency notices received in:
Current year	0	39
Prior years	14,922	45,633
Reinsurance terminations	0	(20)
Total losses paid	14,922	45,652
Net reserve at end of period	810,209	548,997
Plus reinsurance recoverables	102,901	25,756
Reserve at end of period	$ 913,110	$ 574,753