Segment Information - Narrative (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014 segments		Jun. 30, 2013
Segment Reporting Information [Line Items]
Net results from structured products	$ 34,885		$ 6,053		$ 42,838		$ 11,229
Number of segments					2
Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	34,885	[1]	6,053	[2]	42,838	[3]	11,229	[4]
Net investment income | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	16,900		18,100		35,700		35,900
Interest expense | Total P&C
Segment Reporting Information [Line Items]
Net results from structured products	18,200		(12,100)		7,400		(24,600)
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 (credit) of $16.9 million and $(18.2) 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.

[2] The net results from structured products include net investment income and interest expense of $18.1 million and $12.1 million, respectively.

[3] The net results from structured products include net investment income and net interest expense (credit) of $35.7 million and $(7.4) 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 $35.9 million and $24.6 million, respectively.