BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable and Inventories (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Activity in the allowance for doubtful accounts
Beginning balance	$ 611	$ 367	$ 802
Additional reserves	167	333	473
Writeoffs	(414)	(117)	(882)
Effect of foreign currency translation	(2)	28	(26)
Ending balance	362	611	367
Inventories
Parts and raw materials	23,978	23,710
Work-in-process	6,628	2,404
Finished goods	4,928	3,730
Inventory, gross	35,534	29,844
Less reserves	(4,436)	(3,669)
Inventories	31,098	26,175
Provision for excess and obsolete inventory	$ 351	$ 432	$ 753