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, 2020	Sep. 30, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves, beginning of period	$ 1,921,255	$ 1,829,412
Reinsurance recoverables on unpaid losses	76,100	180,859
Net reserves, beginning of period, as adjusted	1,845,304	1,648,553
Incurred losses and loss adjustment expenses related to:
Current year	1,740,116	1,957,598
Prior years	25,511	10,323
Total incurred losses and loss adjustment expenses	1,765,627	1,967,921
Loss and loss adjustment expense payments related to:
Current year	937,373	1,149,659
Prior years	786,180	715,451
Total payments	1,723,553	1,865,110
Net reserves, end of period	1,887,378	1,751,364
Reinsurance recoverables on unpaid losses, end of period	54,608	103,847
Gross reserves, end of period	1,941,986	1,855,211
Cumulative Effect, Period Of Adoption, Adjustment [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables on unpaid losses	(149)	0
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables on unpaid losses	$ 75,951	$ 180,859