Financial Instruments and Investments (Reconciliation) (Details) - Debt Securities - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Fair Value in Investment in Debt Securities [Roll Forward]
Balance at January 1		$ 1,735	$ 1,421
Net unrealized gains (losses) in fair value recognized in income on debt securities still held	[1]	(79)	314
Balance at December 31		$ 1,656	$ 1,735

[1] These amounts are reflected in the Company's statements of operations as investment and interest income.