Allowance For Doubtful Accounts - Rollforward (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]
Beginning Balance	$ 7,220	$ 7,818	$ 6,498
Charged to Costs and Expenses	137	1,375	1,460
Write-Offs Charged to Allowance	(2,206)	(1,949)	(261)
Effect of Exchange Rate Changes	306	(24)	121
Ending Balance	$ 5,457	$ 7,220	$ 7,818