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, 2020	Jun. 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	1,119,502	1,276,235
Prior years	27,468	10,758
Total incurred losses and loss adjustment expenses	1,146,970	1,286,993
Loss and loss adjustment expense payments related to:
Current year	563,921	701,282
Prior years	612,773	557,457
Total payments	1,176,694	1,258,739
Net reserves, end of period	1,815,580	1,676,807
Reinsurance recoverables on unpaid losses, end of period	49,530	107,117
Gross reserves, end of period	1,865,110	1,783,924
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