Reserves for Unpaid Losses and Loss Adjustment Expenses (Activity in the Reserves for Unpaid Losses and Loss Adjustment Expense) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Reserves for Unpaid Losses and Loss Adjustment Expenses [Abstract]
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	257,572	214,080
Loss portfolio transfer	21,700	0
Prior years	33,259	7,781
Total incurred	312,531	221,861
Paid related to:
Current year	67,146	75,834
Loss portfolio transfer	21,700	0
Prior years	177,325	146,929
Total paid	266,171	222,763
Net balance at September 30	394,111	304,629
Plus reinsurance recoverable	361,780	260,667
Balance at September 30	$ 755,891	$ 565,296