(Schedule Of Fair Value Of Financial Instruments) (Details) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		$ 6,546,993	$ 6,069,010
Equity securities		663,390	844,163
Other invested assets		969,427	955,509
Total investments		8,179,810	7,868,682
Senior notes		799,043	798,802
Other long-term debt		23,328	19,213
Total Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets		845,167	812,543
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		6,546,993	6,069,010
Equity securities		663,390	844,163
Other invested assets	[1]	845,167	812,543
Total investments		8,055,550	7,725,716
Senior notes		799,043	798,802
Other long-term debt		23,328	19,213
Fair Value, Measurements, Recurring [Member] | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		28	1,274
Derivative liabilities		9	991
Fair Value, Measurements, Recurring [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		330
Derivative liabilities			683
Fair Value, Measurements, Recurring [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		1,287,748	1,610,502
Fair Value, Measurements, Recurring [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		427,096	188,199
Fair Value, Measurements, Recurring [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		422,007	170,567
Fair Value, Measurements, Recurring [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		2,427,779	2,165,393
Fair Value, Measurements, Recurring [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		1,302,678	1,263,517
Fair Value, Measurements, Recurring [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		679,685	670,832
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		1,225,745	1,499,347
Equity securities		636,576	800,833
Other invested assets	[1]	0	0
Total investments		1,862,321	2,300,180
Senior notes		0	0
Other long-term debt		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | 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 [Member] | Level 1 [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0
Derivative liabilities			0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		1,225,745	1,499,347
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		5,160,029	4,332,467
Equity securities		0	0
Other invested assets	[1]	0	0
Total investments		5,160,029	4,332,467
Senior notes		859,307	879,317
Other long-term debt		28,112	22,583
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		28	1,274
Derivative liabilities		9	991
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		330
Derivative liabilities			683
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		62,003	111,155
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		427,096	188,199
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		422,007	170,567
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		2,427,779	2,165,393
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		1,199,013	1,081,734
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		622,131	615,419
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		161,219	237,196
Equity securities		26,814	43,330
Other invested assets	[1]	0	0
Total investments		188,033	280,526
Senior notes		0	0
Other long-term debt		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | 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 [Member] | Level 3 [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		0
Derivative liabilities			0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		0	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		103,665	181,783
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		57,554	55,413
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		6,546,993	6,069,010
Equity securities		663,390	844,163
Other invested assets	[1]	845,167	812,543
Total investments		8,055,550	7,725,716
Senior notes		859,307	879,317
Other long-term debt		28,112	22,583
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Foreign exchange contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		28	1,274
Derivative liabilities		9	991
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Interest rate swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets		330
Derivative liabilities			683
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		1,287,748	1,610,502
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Non-U.S. Government And Government Agencies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		427,096	188,199
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | States, Municipalities And Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		422,007	170,567
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Corporate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		2,427,779	2,165,393
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		1,302,678	1,263,517
Fair Value, Measurements, Recurring [Member] | Total Fair Value [Member] | Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Trading fixed maturity investments		$ 679,685	$ 670,832

[1] In accordance with U.S. GAAP, other invested assets, excluding other private securities, are measured at fair value using the net asset value per share (or its equivalent) practical expedient and have not been classified in the fair value hierarchy.