Segment Information - Narrative (Details) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2015 USD ($)		Sep. 30, 2014 USD ($)		Sep. 30, 2015 USD ($) segments		Sep. 30, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segments					2
Net results from structured products	$ 4,437	[1]	$ 5,291	[2]	$ 14,719	[3]	$ 48,129	[4]
Net investment income | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	15,600		16,800		46,700		52,500
Interest expense | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	$ (11,100)		$ (11,100)		$ (31,700)		$ (3,700)
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

[1] The net results from P&C structured products include net investment income and interest expense of $15.6 million and $11.1 million, respectively.

[2] The net results from P&C structured products include net investment income and interest credit of $16.8 million and $11.1 million, respectively.

[3] The net results from P&C structured products include net investment income and interest expense of $46.7 million and $31.7 million, respectively.

[4] The net results from P&C structured products include net investment income and interest credit of $52.5 million and $3.7 million, respectively.