Segment Information - Narrative (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014 segments		Sep. 30, 2013
Segment Reporting Information [Line Items]
Net results from structured products	$ 5,291		$ 6,463		$ 48,129		$ 17,692
Number of segments					2
Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	5,291	[1]	6,463	[2]	48,129	[3]	17,692	[4]
Net investment income | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	16,800		18,100		52,500		53,900
Interest expense | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	(11,100)		(11,600)		(3,700)		(36,200)
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
Structured Indemnity [Member] | Interest expense | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products					$ 28,700

[1] The net results from structured products include net investment income and interest expense of $16.8 million and $11.1 million, respectively.

[2] The net results from structured products include net investment income and interest expense of $18.1 million and $11.6 million, respectively.

[3] The net results from structured products include net investment income and net interest expense of $52.5 million and $3.7 million, respectively. Net results from structured products includes a benefit of $28.7 million from a negotiated termination of one of the Company's larger structured indemnity contracts during the second quarter of 2014, producing a net interest expense credit.

[4] The net results from structured products include net investment income and interest expense of $53.9 million and $36.2 million, respectively.