Fair Values of Financial Instruments (Reconciliation of Recurring Fair Value Measurements Recognized in Balance Sheet using Significant Unobservable (Level Three) Inputs) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Values of Financial Instruments [Abstract]
Beginning balance	$ 2,588	$ 2,534	$ 2,522
Total realized and unrealized gains (losses)
Included in other comprehensive income (loss)	133	54	12
Ending balance	$ 2,721	$ 2,588	$ 2,534