Accounts Receivable (Details) - Allowance for Doubtful Accounts [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts, beginning of year	$ 6,457	$ 6,853	$ 8,014
Charges to costs and expenses	2,303	1,460	807
Write-offs of uncollectible accounts, net of recoveries	(1,505)	(1,661)	(1,568)
Currency translation adjustments	375	(195)	(400)
Allowance for doubtful accounts, end of year	$ 7,630	$ 6,457	$ 6,853