Investments (Schedule Of Fair Value Of Investments And Cash And Cash Equivalents) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	$ 540,409		$ 347,632
Unfunded Commitments	245,878
Trading Securities Other	540,409		347,632
Number of long exposure funds	4
Percentage of long exposure greater than fund's net asset value	100.00%
Ratio of the fund's long investments in securities to fund's equity capital	100.00%
Hedge Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net asset value, explicit leverage	145.00%
Mezzanine Debt [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	14,535
Unfunded Commitments	100,344
Trading Securities Other	14,535
Long Exposure (% of funded)	100.00%	[1]
Short Exposure (% of funded)	0.00%	[2]
Gross Exposure	100.00%	[3]
Net Exposure	100.00%	[4]
Equity Long/Short [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Net asset value, explicit leverage	103.00%
Multi-Strategy [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of long exposure funds	2
Net asset value, explicit leverage	103.00%
Event Driven [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Number of long exposure funds	1
Net asset value, explicit leverage	139.00%
Private Equity Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	108,865
Unfunded Commitments	245,878
Trading Securities Other	108,865
Private Equity Funds [Member] | Private Equity Primary And Secondary [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	83,787
Unfunded Commitments	111,566
Trading Securities Other	83,787
Long Exposure (% of funded)	100.00%	[1]
Short Exposure (% of funded)	0.00%	[2]
Gross Exposure	100.00%	[3]
Net Exposure	100.00%	[4]
Private Equity Funds [Member] | Distressed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	10,543
Unfunded Commitments	33,968
Trading Securities Other	10,543
Long Exposure (% of funded)	100.00%	[1]
Short Exposure (% of funded)	0.00%	[2]
Gross Exposure	100.00%	[3]
Net Exposure	100.00%	[4]
Hedge Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	431,544
Trading Securities Other	431,544
Hedge Funds [Member] | Distressed Funds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	42,849
Trading Securities Other	42,849
Long Exposure (% of funded)	61.00%	[1]
Short Exposure (% of funded)	31.00%	[2]
Gross Exposure	92.00%	[3]
Net Exposure	30.00%	[4]
Hedge Funds [Member] | Equity Long/Short [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	159,615
Trading Securities Other	159,615
Long Exposure (% of funded)	75.00%	[1]
Short Exposure (% of funded)	49.00%	[2]
Gross Exposure	124.00%	[3]
Net Exposure	26.00%	[4]
Hedge Funds [Member] | Multi-Strategy [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	157,251
Trading Securities Other	157,251
Long Exposure (% of funded)	98.00%	[1]
Short Exposure (% of funded)	20.00%	[2]
Gross Exposure	118.00%	[3]
Net Exposure	78.00%	[4]
Hedge Funds [Member] | Event Driven [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Fair Value of other invested assets	71,829
Trading Securities Other	$ 71,829
Long Exposure (% of funded)	81.00%	[1]
Short Exposure (% of funded)	66.00%	[2]
Gross Exposure	147.00%	[3]
Net Exposure	15.00%	[4]

[1] Long exposure represents the ratio of the fund's long investments in securities to the fund's equity capital (over 100% may denote explicit borrowing). Four of the Company's hedge funds, two multi-strategy funds, one event driven fund and one equity long/short fund had long exposure greater than 100% of the funds' net asset value (indicating explicit leverage). The funds had long exposure of 145%, 103%, 139% and 103%, respectively, as of December 31, 2011.

[2] Short exposure represents the ratio of the fund's equity to securities sold short.

[3] Gross exposure is the addition of the long and short exposures.

[4] Net exposure is the subtraction of the short exposure from the long exposure.