Segment Information - Narrative (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 segments	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Number of Operating Segments	2
Net results from structured products	$ 54,209	$ 23,791	$ 5,257
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
Total P And C Segment [Member] | Net Investment Income [Member]
Segment Reporting Information [Line Items]
Net results from structured products	68,000	71,900	71,700
Total P And C Segment [Member] | Interest Expense [Member]
Segment Reporting Information [Line Items]
Net results from structured products	$ (12,900)	$ (48,000)	$ (66,300)