Investments (Schedule Of Trading Securities) (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Equity securities and other invested assets [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	$ 1,508,557	$ 1,656,706
Trading securities, Amortized Cost	1,430,853	1,516,275
Equity securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	663,390	844,163
Trading securities, Amortized Cost	668,061	791,206
Other invested assets [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	845,167	812,543
Trading securities, Amortized Cost	762,792	725,069
Fixed maturity investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	6,546,993	6,069,010
Trading securities, Amortized Cost	6,555,748	6,035,240
U.S. Government And Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,287,749	1,610,502
Trading securities, Amortized Cost	1,283,085	1,610,880
Non-U.S. Government And Government Agencies [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	427,096	188,199
Trading securities, Amortized Cost	449,572	196,332
States, Municipalities And Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	422,007	170,567
Trading securities, Amortized Cost	410,052	165,615
Corporate Debt, Financial Institutions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,052,636	1,024,667
Trading securities, Amortized Cost	1,049,451	1,018,777
Corporate Debt, Industrials [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,256,975	1,029,729
Trading securities, Amortized Cost	1,276,413	1,037,820
Corporate Debt, Utilities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	118,167	110,997
Trading securities, Amortized Cost	120,856	111,599
Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	1,302,678	1,263,517
Trading securities, Amortized Cost	1,273,349	1,219,712
Asset-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading securities, Fair Value	679,685	670,832
Trading securities, Amortized Cost	$ 692,970	$ 674,505