Segment Information (Details) - Narrative (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 segments		Dec. 31, 2011		Dec. 31, 2010
Segment Reporting Information [Line Items]
Number of Operating Segments	3
Net results from structured products	$ 5,098	[1]	$ 23,029	[1]	$ 27,575	[2]
Alternative funds
Segment Reporting Information [Line Items]
Alternative investments, timelag for reporting	1 month
Operating affiliates
Segment Reporting Information [Line Items]
Alternative investments, timelag for reporting	3 months
Net Investment Income [Member]
Segment Reporting Information [Line Items]
Net results from structured products					12,500
Interest Expense [Member]
Segment Reporting Information [Line Items]
Net results from structured products					(1,700)
Operating Expenses [Member]
Segment Reporting Information [Line Items]
Net results from structured products					(1,000)
Total P And C Segment [Member]
Segment Reporting Information [Line Items]
Net results from structured products	5,098	[1]	23,029	[1]	17,771	[2]
Total P And C Segment [Member] | Net Investment Income [Member]
Segment Reporting Information [Line Items]
Net results from structured products	71,700		74,600		69,000
Total P And C Segment [Member] | Interest Expense [Member]
Segment Reporting Information [Line Items]
Net results from structured products	(66,400)		(51,500)		(52,900)
Total P And C Segment [Member] | Operating Expenses [Member]
Segment Reporting Information [Line Items]
Net results from structured products					1,600
Corporate And Other [Member]
Segment Reporting Information [Line Items]
Net results from structured products					$ 9,804	[2]

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

[2] The net results from P&C structured products include net investment income, interest expense and operating expenses.