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	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Values of Financial Instruments [Abstract]
Beginning balance	$ 2,721	$ 2,588
Total realized and unrealized gains (losses)
Included in net income
Included in other comprehensive income (loss)
Purchases, sales, issuances and settlements
Ending balance	$ 2,721	$ 2,588