Segment Information (Details) - Narrative (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012 segments		Sep. 30, 2011
Segment Reporting Information [Line Items]
Number of Operating Segments					3
Net results from structured products	$ 5,701	[1]	$ 5,845	[1]	$ (2,848)	[1]	$ 18,235	[1]
Alternative Funds [Member]
Segment Reporting Information [Line Items]
Investment income, time lag for reporting	1 month				1 month
Private Investment And Operating Fund Affiliates [Member]
Segment Reporting Information [Line Items]
Investment income, time lag for reporting	3 months				3 months
Total P And C Segment [Member]
Segment Reporting Information [Line Items]
Net results from structured products	5,701	[1]	5,845	[1]	(2,848)	[1]	18,235	[1]
Total P And C Segment [Member] | Net Investment Income [Member]
Segment Reporting Information [Line Items]
Net results from structured products	17,400		18,900		52,200	[1]	57,000
Total P And C Segment [Member] | Interest Expense [Member]
Segment Reporting Information [Line Items]
Net results from structured products	$ (11,700)		$ (13,000)		$ (55,000)		$ (38,800)

[1] The net results from P&C structured products include net investment income and interest expense.