Other Income and Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Other income (expense)
Foreign exchange transaction gain (loss)	$ 1,289	$ (128)	$ 249	$ (700)
Government subsidy income	269	75	269	75
Other non-operating gain	19	108	31	121
Gain (loss) on disposal of assets	4	9	5	(40)
Other income and expense, net	$ 1,581	$ 64	$ 554	$ (544)