Accounts Receivable, Net and Revenue Concentrations - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Schedule of Allowance for Doubtful Accounts
Balance at beginning of period	$ 1,121	$ 1,064
Additions to costs and expenses	5	2
(Write-offs)/Foreign exchange effects	(4)	(58)
Balance at end of period	$ 1,122	$ 1,008