Loss And Loss Adjustment Expense Reserves (Activity In The Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves, beginning of period	$ 1,991,304	$ 1,921,255
Reinsurance recoverables on unpaid losses	54,460	76,100
Net reserves, beginning of period, as adjusted	1,936,844	1,845,304
Incurred losses and loss adjustment expenses related to:
Current year	2,005,233	1,740,116
Prior years	(23,714)	25,511
Total incurred losses and loss adjustment expenses	1,981,519	1,765,627
Loss and loss adjustment expense payments related to:
Current year	1,088,285	937,373
Prior years	739,385	786,180
Total payments	1,827,670	1,723,553
Net reserves, end of period	2,090,693	1,887,378
Reinsurance recoverables on unpaid losses, end of period	51,428	54,608
Gross reserves, end of period	2,142,121	1,941,986
Cumulative Effect, Period Of Adoption, Adjustment [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables on unpaid losses	0	(149)
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables on unpaid losses	$ 54,460	$ 75,951