Reserves for Losses and Loss Adjustment Expenses (Activity in the Reserves for Unpaid Losses and Loss Adjustment Expense) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Reserves for Losses and Loss Adjustment Expenses
Balance at January 1	$ 620,355	$ 527,247
Less reinsurance recoverable	272,604	221,716
Net balance at January 1	347,751	305,531
Incurred related to:
Current year	332,863	301,265
Loss portfolio transfer	21,700	0
Prior years	58,288	60,900
Total incurred	412,851	362,165
Paid related to:
Current year	113,312	127,610
Loss portfolio transfer	21,700	0
Prior years	185,407	192,335
Total paid	320,419	319,945
Net balance at December 31	440,183	347,751
Plus reinsurance recoverable	349,585	272,604
Balance at December 31	$ 789,768	$ 620,355