Investments (Schedule Of Investments And Cash And Cash Equivalents) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2011		Dec. 31, 2010
Investment [Line Items]
Fair value of other invested assets	$ 552,074		$ 347,632
Unfunded Commitments	310,175
Ratio of the fund's long investments in securities to fund's equity capital	100.00%
Percentage of gross exposure addition of long and short exposure	100.00%
Private Equity Funds [Member]
Investment [Line Items]
Fair value of other invested assets	78,078
Unfunded Commitments	162,162
Long Exposure	100.00%	[1]
Short Exposure	0.00%	[2]
Gross Exposure	100.00%	[3]
Net Exposure	100.00%	[4]
Mezzanine Debt [Member]
Investment [Line Items]
Fair value of other invested assets	3,308
Unfunded Commitments	111,621
Long Exposure	100.00%	[1]
Short Exposure	0.00%	[2]
Gross Exposure	100.00%	[3]
Net Exposure	100.00%	[4]
Distressed [Member]
Investment [Line Items]
Fair value of other invested assets	8,744
Unfunded Commitments	36,392
Long Exposure	100.00%	[1]
Short Exposure	0.00%	[2]
Gross Exposure	100.00%	[3]
Net Exposure	100.00%	[4]
Total Private Equity [Member]
Investment [Line Items]
Fair value of other invested assets	90,130
Unfunded Commitments	310,175
Distressed Hedge Funds [Member]
Investment [Line Items]
Fair value of other invested assets	46,767
Long Exposure	64.00%	[1]
Short Exposure	42.00%	[2]
Gross Exposure	106.00%	[3]
Net Exposure	22.00%	[4]
Equity Long/Short [Member]
Investment [Line Items]
Fair value of other invested assets	175,170
Long Exposure	78.00%	[1]
Short Exposure	58.00%	[2]
Gross Exposure	136.00%	[3]
Net Exposure	20.00%	[4]
Multi-Strategy [Member]
Investment [Line Items]
Fair value of other invested assets	157,479
Long Exposure	88.00%	[1]
Short Exposure	66.00%	[2]
Gross Exposure	154.00%	[3]
Net Exposure	22.00%	[4]
Number of long exposure funds	1
Net asset value, explicit leverage	110.00%
Hedge Funds [Member]
Investment [Line Items]
Number of long exposure funds	2
Event Driven [Member]
Investment [Line Items]
Fair value of other invested assets	$ 82,528
Long Exposure	93.00%	[1]
Short Exposure	69.00%	[2]
Gross Exposure	162.00%	[3]
Net Exposure	24.00%	[4]
Number of long exposure funds	1
Net asset value, explicit leverage	140.00%

[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). Two of the Company's hedge funds, one event driven fund and one multi-strategy fund had long exposure greater than 100% of the funds' net asset value (indicating explicit leverage) of 140% and 110%, respectively, as of September 30, 2011.

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

[3] Gross exposure is the addition of the long and short exposures (over 100% may denote explicit borrowing).

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