Investments (Schedule Of Other Investments) (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2015	Dec. 31, 2014
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 896,790	$ 955,509
Unfunded Commitments		591,882	483,214
Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		387,392	527,519
Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 338,540	427,990
Investments without redemption restrictions [Member] | Hedge Funds [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period		30 days
Total Fair Value [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 769,173	812,543
Unfunded Commitments		591,882	483,214
Total Fair Value [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		387,392	357,350
Unfunded Commitments		591,882	483,214
Total Fair Value [Member] | Private Equity [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		198,302	184,576
Unfunded Commitments		180,988	223,802
Total Fair Value [Member] | Mezzanine Debt [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		183,002	166,905
Unfunded Commitments		255,333	204,232
Total Fair Value [Member] | Distressed [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		6,088	5,869
Unfunded Commitments		5,561	5,180
Total Fair Value [Member] | Real Estate [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Unfunded Commitments		150,000	50,000
Total Fair Value [Member] | Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		351,900	425,030
Unfunded Commitments		0	0
Total Fair Value [Member] | Distressed Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		170,858	170,169
Unfunded Commitments		0	0
Total Fair Value [Member] | Equity Long/Short [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		60,103	84,198
Unfunded Commitments		0	0
Total Fair Value [Member] | Multi-Strategy Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			51,507
Unfunded Commitments			0
Total Fair Value [Member] | Relative Value Credit [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		120,939	119,156
Unfunded Commitments		0	0
Total Fair Value [Member] | High Yield Loan Fund [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		29,881	30,163
Unfunded Commitments		0	0
Total Fair Value [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		387,392	527,519
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		387,392	357,350
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Private Equity [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 198,302	$ 184,576
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Private Equity [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		2 years	2 years
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Private Equity [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		8 years	8 years
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Mezzanine Debt [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 183,002	$ 166,905
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Mezzanine Debt [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		5 years	5 years
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Mezzanine Debt [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period		9 years	9 years
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Distressed [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 6,088	$ 5,869
Estimated remaining restriction period		3 years	3 years
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Real Estate [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 0	$ 0
Estimated remaining restriction period		9 years	9 years
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 0	$ 170,169
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Distressed Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	$ 170,169
Estimated remaining restriction period			1 year
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Equity Long/Short [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	$ 0
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Multi-Strategy Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			0
Total Fair Value [Member] | Investments with redemption restrictions [Member] | Relative Value Credit [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value [Member] | Investments with redemption restrictions [Member] | High Yield Loan Fund [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		210,923	285,024
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Private Equity [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Mezzanine Debt [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Distressed [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Real Estate [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		181,042	254,861
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Distressed Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 0	$ 0
Redemption frequency	[1]	Based on net asset value	Based on net asset value
Redemption notice period	[1]	60 days	60 days
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Equity Long/Short [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 60,103	$ 84,198
Redemption frequency	[1]	Quarterly	Quarterly
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Equity Long/Short [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	[1]	30 days	30 days
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Equity Long/Short [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	[1]	60 days	60 days
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Multi-Strategy Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets			$ 51,507
Redemption frequency	[1]		Quarterly
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Multi-Strategy Funds [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	[1]		45 days
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Multi-Strategy Funds [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	[1]		90 days
Total Fair Value [Member] | Investments without redemption restrictions [Member] | Relative Value Credit [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 120,939	$ 119,156
Redemption frequency	[1]	Quarterly	Quarterly
Redemption notice period	[1]	60 days	60 days
Total Fair Value [Member] | Investments without redemption restrictions [Member] | High Yield Loan Fund [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 29,881	$ 30,163
Redemption frequency	[1]	Monthly	Monthly
Redemption notice period	[1]	30 days	30 days
Carrying Value [Member] | Other Private Securities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 127,617	$ 142,966
Unfunded Commitments		0	0
Carrying Value [Member] | Investments with redemption restrictions [Member] | Other Private Securities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		0	0
Carrying Value [Member] | Investments without redemption restrictions [Member] | Other Private Securities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets		$ 127,617	$ 142,966

[1] The redemption frequency and notice periods only apply to the investments without redemption restrictions. Some or all of these investments may be subject to a gate as described below.