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, 2018	Dec. 31, 2017	Dec. 31, 2016
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	$ 9,006,199
Reinsurance recoverable on unpaid losses	5,062,036
Unallocated loss adjustment expenses	239,753
Unamortized fair value adjustments on acquired reserves for losses and loss adjustment expenses	(31,509)
Total reconciling items	208,244
Total gross liability for unpaid losses and loss adjustment expenses	14,276,479	$ 13,584,281	$ 10,115,662
Insurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	5,765,438
Reinsurance recoverable on unpaid losses	1,965,565
Total gross liability for unpaid losses and loss adjustment expenses	7,947,772	7,711,510
Reinsurance [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	3,034,131
Reinsurance recoverable on unpaid losses	415,900
Total gross liability for unpaid losses and loss adjustment expenses	3,425,751	3,248,070
Other Insurance (Discontinued Lines) [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	204,069
Reinsurance recoverable on unpaid losses	166,505
Program Services [Member]
Short-duration Insurance Contracts, Reconciliation of Claims Development to Liability [Line Items]
Liabilities for for unpaid losses and loss adjustment expenses, net of reinsurance	2,561
Reinsurance recoverable on unpaid losses	2,514,066
Total gross liability for unpaid losses and loss adjustment expenses	$ 2,516,627	$ 2,195,431