Investments (Summary of Realized Gain (Loss) on Investments) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Schedule of Investments [Line Items]
(Loss) gain on investments	$ (15)	$ 2,501
Net realized (losses) gains	(4,835)	2,060
Other Investments [Member]
Schedule of Investments [Line Items]
Unrealized losses on other investments	(363)	(441)
Us Treasury Securities and Obligations of U.S. Government [Member]
Schedule of Investments [Line Items]
(Loss) gain on investments
Corporate Bonds [Member]
Schedule of Investments [Line Items]
(Loss) gain on investments	(8)	130
Collateralized Corporate Bank Loans [Member]
Schedule of Investments [Line Items]
(Loss) gain on investments	12	28
Municipal Bonds [Member]
Schedule of Investments [Line Items]
(Loss) gain on investments	(21)	(17)
Mortgage Backed [Member]
Schedule of Investments [Line Items]
(Loss) gain on investments	2
Equity Securities [Member]
Schedule of Investments [Line Items]
(Loss) gain on investments		$ 2,360
Unrealized losses on other investments	$ (4,457)