Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Consolidated Reserves For Losses And Loss Adjustment Expenses) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims [Abstract]
Net reserves for losses and loss adjustment expenses, beginning of year			$ 9,214,443	$ 8,964,945
Foreign currency movements	$ (51,544)	$ (35,754)	(51,544)	(35,754)
Adjusted net reserves for losses and loss adjustment expenses, beginning of year			9,162,899	8,929,191
Net losses and loss adjustment expenses	900,230	860,986	2,454,912	2,340,868
Incurred losses and loss adjustment expenses, prior accident years			(336,942)	(389,740)
Total incurred losses and loss adjustment expenses			2,117,970	1,951,128
Payments, current accident year			410,493	390,245
Payments, prior accident years			1,597,117	1,438,224
Total payments			2,007,610	1,828,469
Effect of foreign currency rate changes			(669)	368
Net reserves for losses and loss adjustment expenses, end of period	9,272,590	9,052,218	9,272,590	9,052,218
Reinsurance recoverable on unpaid losses	5,165,226	4,836,271	5,165,226	4,836,271
Gross reserves for losses and loss adjustment expenses, end of period	$ 14,437,816	$ 13,888,489	$ 14,437,816	$ 13,888,489