Segment Information - Narrative (Details) $ in Thousands		12 Months Ended
		Dec. 31, 2017 USD ($) segments		Dec. 31, 2016 USD ($)		Dec. 31, 2015 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segments		2
Net results from structured products		$ 26,428	[1]	$ 14,280	[2]	$ 17,991	[3]
Other Operating Income (Expense), Net	[4]	(2,076)		(13,315)		(13,356)
Property and casualty operations | Net Investment Income [Member]
Segment Reporting Information [Line Items]
Net results from structured products		51,700		54,000		60,400
Property and casualty operations | Interest expense
Segment Reporting Information [Line Items]
Net results from structured products		(25,300)		(39,700)		(42,200)
Other Operating Income (Expense) [Member]
Segment Reporting Information [Line Items]
Other Operating Income (Expense), Net		$ (50,700)		$ (49,000)		$ (46,600)

[1] The net results from P&C structured products include net investment income and interest expense of $51.7 million and $25.3 million, respectively.

[2] The net results from P&C structured products include net investment income and interest expense of $54.0 million and $39.7 million, respectively.

[3] The net results from P&C structured products include net investment income and interest expense of $60.4 million and $42.2 million, respectively.

[4] Net fee income and other includes operating expenses of $50.7 million from the Company's loss prevention consulting services business.