Loss Reserves - Reconciliation of Changes in Loss Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loss Reserve [Roll Forward]
Reserve at beginning of year	$ 880,537	$ 555,334	$ 674,019
Less reinsurance recoverable	66,905	95,042	21,641	$ 33,328
Net reserve at beginning of year	816,617	785,495	533,693	$ 640,691
Losses incurred: [Abstract]
Current year	124,592	345,170	189,581
Prior years	(60,015)	19,604	(71,006)
Total losses incurred	64,577	364,774	118,575
Losses paid [Abstract]
Current year	664	3,069	4,018
Prior years	68,769	109,923	235,551
Reinsurance terminations	(35,978)	(20)	(13,996)
Total losses paid	33,455	112,972	225,573
Reserve at end of year	$ 883,522	$ 880,537	$ 555,334