Loss And Loss Adjustment Expense Reserves (Activity In The Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 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	1,298,981	1,119,502
Prior years	(15,409)	27,468
Total incurred losses and loss adjustment expenses	1,283,572	1,146,970
Loss and loss adjustment expense payments related to:
Current year	641,726	563,921
Prior years	539,871	612,773
Total payments	1,181,597	1,176,694
Net reserves, end of period	2,038,819	1,815,580
Reinsurance recoverables on unpaid losses, end of period	52,196	49,530
Gross reserves, end of period	2,091,015	1,865,110
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