Accounts Receivable, Net and Revenue Concentrations - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Allowance for Doubtful Accounts
Balance at beginning of period	$ 904	$ 822	$ 616
Additions to costs and expenses	166	183	299
(Write-offs)/Foreign exchange effects	(6)	(101)	(93)
Balance at end of period	$ 1,064	$ 904	$ 822