Fair Value Of Financial Instruments (Schedule Of Fair Value Of Financial Instruments) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	$ 6,069,010	$ 6,100,798
Equity securities	844,163	699,846
Other invested assets	955,509	911,392
Total investments	7,868,682	7,712,036
Senior notes	798,802	798,499
Other long-term debt	19,213	0
Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets	812,543	764,081
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	6,069,010	6,100,798
Equity securities	844,163	699,846
Other invested assets	812,543	764,081
Total investments	7,725,716	7,564,725
Senior notes	798,802	798,499
Other long-term debt	19,213
Fair Value, Measurements, Recurring | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	1,274	6,254
Derivative liabilities	991	1,176
Fair Value, Measurements, Recurring | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		6,829
Derivative liabilities	683	4,214
Fair Value, Measurements, Recurring | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,610,502	1,676,788
Fair Value, Measurements, Recurring | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	188,199	191,776
Fair Value, Measurements, Recurring | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	170,567	231,555
Fair Value, Measurements, Recurring | Corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	2,165,393	2,202,267
Fair Value, Measurements, Recurring | Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,263,517	1,292,502
Fair Value, Measurements, Recurring | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	670,832	505,910
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,499,347	1,370,088
Equity securities	800,833	625,942
Other invested assets	0	0
Total investments	2,300,180	1,996,030
Senior notes	0	0
Other long-term debt	0
Fair Value, Measurements, Recurring | Level 1 | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 1 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 1 | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,499,347	1,370,088
Fair Value, Measurements, Recurring | Level 1 | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 1 | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	4,332,467	4,489,959
Equity securities	0	0
Other invested assets	0	0
Total investments	4,332,467	4,489,959
Senior notes	879,317	897,601
Other long-term debt	22,583
Fair Value, Measurements, Recurring | Level 2 | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	1,274	6,254
Derivative liabilities	991	1,176
Fair Value, Measurements, Recurring | Level 2 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		6,829
Derivative liabilities	683	4,214
Fair Value, Measurements, Recurring | Level 2 | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	111,155	306,700
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	188,199	191,776
Fair Value, Measurements, Recurring | Level 2 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	170,567	231,555
Fair Value, Measurements, Recurring | Level 2 | Corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	2,165,393	2,202,267
Fair Value, Measurements, Recurring | Level 2 | Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,081,734	1,145,164
Fair Value, Measurements, Recurring | Level 2 | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	615,419	412,497
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	237,196	240,751
Equity securities	43,330	73,904
Other invested assets	812,543	764,081
Total investments	1,093,069	1,078,736
Senior notes	0	0
Other long-term debt	0
Fair Value, Measurements, Recurring | Level 3 | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 3 | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0
Derivative liabilities	0	0
Fair Value, Measurements, Recurring | Level 3 | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | Corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	0	0
Fair Value, Measurements, Recurring | Level 3 | Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	181,783	147,338
Fair Value, Measurements, Recurring | Level 3 | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	55,413	93,413
Fair Value, Measurements, Recurring | Total Fair Value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	6,069,010	6,100,798
Equity securities	844,163	699,846
Other invested assets	812,543	764,081
Total investments	7,725,716	7,564,725
Senior notes	879,317	897,601
Other long-term debt	22,583
Fair Value, Measurements, Recurring | Total Fair Value | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets	1,274	6,254
Derivative liabilities	991	1,176
Fair Value, Measurements, Recurring | Total Fair Value | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		6,829
Derivative liabilities	683	4,214
Fair Value, Measurements, Recurring | Total Fair Value | U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,610,502	1,676,788
Fair Value, Measurements, Recurring | Total Fair Value | Non-U.S. Government and Government Agencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	188,199	191,776
Fair Value, Measurements, Recurring | Total Fair Value | States, municipalities and political subdivisions
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	170,567	231,555
Fair Value, Measurements, Recurring | Total Fair Value | Corporate debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	2,165,393	2,202,267
Fair Value, Measurements, Recurring | Total Fair Value | Mortgage-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	1,263,517	1,292,502
Fair Value, Measurements, Recurring | Total Fair Value | Asset-backed
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments	$ 670,832	$ 505,910