Loss And Loss Adjustment Expense Reserves (Activity In The Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves at January 1	$ 1,921,255	$ 1,829,412	$ 1,510,613
Reinsurance recoverables on unpaid losses	54,460	76,100	180,859	$ 64,001
Net reserves at January 1	1,845,155	1,648,553	1,446,612
Incurred losses and loss adjustment expense related to:
Current year	2,372,364	2,696,230	2,483,693
Prior year claims and claim adjustment expense	22,979	9,794	93,096
Total incurred losses and loss adjustment expenses	2,395,343	2,706,024	2,576,789
Loss and loss adjustment expense payments related to:
Current year	1,366,661	1,651,550	1,543,828
Prior years	937,142	857,872	831,020
Total payments	2,303,803	2,509,422	2,374,848
Net reserves at December 31	1,936,844	1,845,155	1,648,553
Gross reserves at December 31	1,991,304	1,921,255	1,829,412
Cumulative Effect, Period of Adoption, Adjustment
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables on unpaid losses		(149)	0	0
Cumulative Effect, Period of Adoption, Adjusted Balance
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables on unpaid losses		75,951	$ 180,859	$ 64,001
Net reserves at January 1	$ 1,845,304
Loss and loss adjustment expense payments related to:
Net reserves at December 31		$ 1,845,304