Segment Information - Narrative (Details) $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2015 USD ($)		Jun. 30, 2014 USD ($)		Jun. 30, 2015 USD ($) segments		Jun. 30, 2014 USD ($)
Segment Reporting Information [Line Items]
Number of segments | segments					2
Net results from structured products	$ (5,257)	[1]	$ (34,885)	[2]	$ (10,282)	[3]	$ (42,838)	[4]
Net investment income | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	(16,000)		(16,900)		(31,100)		(35,700)
Interest expense | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	$ 10,600		$ (18,200)		$ 20,600		$ (7,400)
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 $16.0 million and $10.6 million, respectively.

[2] The net results from P&C structured products include net investment income and interest credit of $16.9 million and $18.2 million, respectively.

[3] The net results from P&C structured products include net investment income and interest expense of $31.1 million and $20.6 million, respectively.

[4] The net results from P&C structured products include net investment income and interest credit of $35.7 million and $7.4 million, respectively.