Schedule Of Valuation And Qualifying Accounts (Tables) (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	$ 2,838	$ 3,417	$ 2,943
Charges to Operatons	1,697	0	499
Other additions	0	0	0
Deductions	4,430	579	25
Balance at end of period	$ 105	$ 2,838	$ 3,417