Loss And Loss Adjustment Expense Reserves (Activity In The Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Gross reserves, beginning of period	$ 1,921,096	$ 1,829,412
Reinsurance recoverables on unpaid losses	(76,100)	(180,859)
Net reserves, beginning of period	1,845,155	1,648,553
Incurred losses and loss adjustment expenses related to:
Current year	636,566	629,054
Prior years	15,104	1,362
Total incurred losses and loss adjustment expenses	651,670	630,416
Loss and loss adjustment expense payments related to:
Current year	264,658	274,273
Prior years	403,436	344,718
Total payments	668,094	618,991
Net reserves, end of period	1,828,731	1,659,978
Reinsurance recoverables on unpaid losses	69,214	127,634
Gross reserves, end of period	1,897,945	1,787,612
Cumulative Effect, Period Of Adoption, Adjustment [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables on unpaid losses	159	0
Cumulative Effect, Period Of Adoption, Adjusted Balance [Member]
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Reinsurance recoverables on unpaid losses	$ (75,941)	$ (180,859)