Valuation And Qualifying Accounts (Details) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 1,816	$ 1,796	$ 1,319
Additions, Charged to Costs and Expenses	70	1	516
Deductions	17	(19)	39
Balance at End of Period	$ 1,869	$ 1,816	$ 1,796