Unpaid Losses And Loss Adjustment Expenses (Reconciliation Of Net Incurred And Paid Loss Development Tables, By Segment, To The Liability For Losses And Loss Adjustment Expenses In The Consolidated Balance Sheet) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	$ 9,253,056
Reinsurance recoverable on unpaid losses	5,253,415
Unallocated loss adjustment expenses	264,029
Unamortized discount, net of acquisition fair value adjustments, included in unpaid losses and loss adjustment expenses	(41,824)
Total reconciling items	222,205
Total gross liability for unpaid losses and loss adjustment expenses	14,728,676	$ 14,276,479	$ 13,584,281
Insurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	6,041,424
Reinsurance recoverable on unpaid losses	1,838,552
Total gross liability for unpaid losses and loss adjustment expenses	8,119,046	7,947,772
Reinsurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	3,075,109
Reinsurance recoverable on unpaid losses	349,124
Total gross liability for unpaid losses and loss adjustment expenses	3,395,459	3,425,751
Other Underwriting [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	134,299
Reinsurance recoverable on unpaid losses	155,714
Total gross liability for unpaid losses and loss adjustment expenses	298,062	386,329
Program Services and Other [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for unpaid losses and loss adjustment expenses, net of reinsurance	2,224
Reinsurance recoverable on unpaid losses	2,910,025
Total gross liability for unpaid losses and loss adjustment expenses	$ 2,916,109	$ 2,516,627