Reserve for Losses and Loss Expenses (Roll Forward of Gross and Net Environmental Incurred Losses and Loss Expenses and Related Reserves) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reserves for losses and loss expenses at beginning of year, gross	$ 36,012	$ 43,609	$ 46,920
Incurred losses and loss expenses, gross	3,059	(2,271)	1,162
Less: losses and loss expenses paid, gross	(3,496)	(5,326)	(4,473)
Reserves for losses and loss expenses at the end of year, gross	35,575	36,012	43,609
Reserves for losses and loss expenses at beginning of year, net	27,916	35,766	38,047
Incurred losses and loss expenses, net	3,000	(2,750)	1,938
Less: losses and loss expenses paid, net	(3,147)	(5,100)	(4,219)
Reserves for losses and loss expenses at the end of year, net	27,769	27,916	35,766
Asbestos [Member]
Reserves for losses and loss expenses at beginning of year, gross	8,412	9,979	11,056
Incurred losses and loss expenses, gross	1,696	2,014	(338)
Less: losses and loss expenses paid, gross	(938)	(3,581)	(739)
Reserves for losses and loss expenses at the end of year, gross	9,170	8,412	9,979
Reserves for losses and loss expenses at beginning of year, net	6,586	8,167	9,244
Incurred losses and loss expenses, net	2,000	2,000	(338)
Less: losses and loss expenses paid, net	(795)	(3,581)	(739)
Reserves for losses and loss expenses at the end of year, net	7,791	6,586	8,167
Enviromental [Member]
Reserves for losses and loss expenses at beginning of year, gross	27,600	33,630	35,864
Incurred losses and loss expenses, gross	1,363	(4,285)	1,500
Less: losses and loss expenses paid, gross	(2,558)	(1,745)	(3,734)
Reserves for losses and loss expenses at the end of year, gross	26,405	27,600	33,630
Reserves for losses and loss expenses at beginning of year, net	21,330	27,599	28,803
Incurred losses and loss expenses, net	1,000	(4,750)	2,276
Less: losses and loss expenses paid, net	(2,352)	(1,519)	(3,480)
Reserves for losses and loss expenses at the end of year, net	$ 19,978	$ 21,330	$ 27,599