Investments (Schedule Of Other Investments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2014		Dec. 31, 2013
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	$ 989,791		$ 911,392
Unfunded Commitments	450,261		467,524
Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	448,990		368,052
Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	540,801		543,340
Hedge Funds [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P30D
Portion at Fair Value, Fair Value Disclosure [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	839,987		764,081
Unfunded Commitments	450,261		467,524
Portion at Fair Value, Fair Value Disclosure [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	448,990		368,052
Portion at Fair Value, Fair Value Disclosure [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	390,997		396,029
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	235,808		216,825
Unfunded Commitments	450,261		467,524
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	235,808		216,825
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	144,582		144,422
Unfunded Commitments	262,450		263,519
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	144,582		144,422
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity [Member] | Investments with redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	2 years		2 years
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity [Member] | Investments with redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	9 years		9 years
Portion at Fair Value, Fair Value Disclosure [Member] | Private Equity [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Mezzanine Debt [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	81,474		64,627
Unfunded Commitments	182,562		198,756
Portion at Fair Value, Fair Value Disclosure [Member] | Mezzanine Debt [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	81,474		64,627
Portion at Fair Value, Fair Value Disclosure [Member] | Mezzanine Debt [Member] | Investments with redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	8 years		8 years
Portion at Fair Value, Fair Value Disclosure [Member] | Mezzanine Debt [Member] | Investments with redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period	9 years		9 years
Portion at Fair Value, Fair Value Disclosure [Member] | Mezzanine Debt [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	9,752		7,776
Unfunded Commitments	5,249		5,249
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	9,752		7,776
Estimated remaining restriction period	4 years		4 years
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Hedge Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	571,259		515,298
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Hedge Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	213,182		151,227
Portion at Fair Value, Fair Value Disclosure [Member] | Hedge Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	358,077		364,071
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	161,033		151,227
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	161,033		151,227
Estimated remaining restriction period	1 year
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed Funds [Member] | Investments with redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period			1 year
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed Funds [Member] | Investments with redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Estimated remaining restriction period			2 years
Portion at Fair Value, Fair Value Disclosure [Member] | Distressed Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Equity Long/Short [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	163,964		99,365
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Equity Long/Short [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	52,149		0
Estimated remaining restriction period	1 year
Portion at Fair Value, Fair Value Disclosure [Member] | Equity Long/Short [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	111,815		99,365
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Equity Long/Short [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P30D	[1]	P30D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Equity Long/Short [Member] | Investments without redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P60D	[1]	P60D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Multi-Strategy Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	122,584		136,958
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Multi-Strategy Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	122,584		136,958
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member] | Minimum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P45D	[1]	P45D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Multi-Strategy Funds [Member] | Investments without redemption restrictions [Member] | Maximum [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Redemption notice period	P90D	[1]	P90D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Event Driven Funds [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	6,407		14,018
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Event Driven Funds [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Event Driven Funds [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	6,407		14,018
Redemption frequency	Annual	[1]	Annual	[1]
Redemption notice period	P60D	[1]	P60D	[1]
Portion at Fair Value, Fair Value Disclosure [Member] | Relative Value Credit [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	117,271		113,730
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Relative Value Credit [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | Relative Value Credit [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	117,271		113,730
Redemption frequency	Quarterly	[1]	Quarterly	[1]
Redemption notice period	P60D	[1]	P60D
Portion at Fair Value, Fair Value Disclosure [Member] | High Yield Loan Fund [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	32,920		31,958
Unfunded Commitments	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | High Yield Loan Fund [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Portion at Fair Value, Fair Value Disclosure [Member] | High Yield Loan Fund [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	32,920		31,958
Redemption frequency	Monthly	[1]	Monthly	[1]
Redemption notice period	P30D	[1]	P30D	[1]
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Other Private Securities [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	149,804		147,311
Unfunded Commitments	0		0
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Other Private Securities [Member] | Investments with redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	0		0
Carrying (Reported) Amount, Fair Value Disclosure [Member] | Other Private Securities [Member] | Investments without redemption restrictions [Member]
Fair Value, Investments, Entities that Calculate Net Asset Value Per Share [Line Items]
Other invested assets	$ 149,804		$ 147,311

[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.