Segment Information - Narrative (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013 segments		Jun. 30, 2012
Segment Reporting Information [Line Items]
Net results from structured products	$ 6,053	[1]	$ (13,759)	[2]	$ 11,229	[3]	$ (8,502)	[4]
Number of segments					3
Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	6,053	[1]	(13,759)	[2]	11,229	[3]	(8,502)	[4]
Net investment income | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	18,100		17,400		35,900		34,700
Interest expense | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	$ (12,100)		$ (31,200)		$ (24,600)		$ (43,200)
Alternative funds
Segment Reporting Information [Line Items]
Alternative investments, timelag for reporting	1 month		1 month
Operating affiliates
Segment Reporting Information [Line Items]
Alternative investments, timelag for reporting	3 months		3 months

[1] The net results from P&C structured products include net investment income and interest expense of $18.1 million and $12.1 million, respectively

[2] The net results from P&C structured products include net investment income and interest expense of $17.4 million and $31.2 million, respectively.

[3] The net results from P&C structured products include net investment income and interest expense of $35.9 million and $24.6 million, respectively.

[4] The net results from P&C structured products include net investment income and interest expense of $34.7 million and $43.2 million, respectively.