BUSINESS AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable and Inventories (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Activity in the allowance for doubtful accounts
Beginning balance	$ 362	$ 611	$ 367
Additional reserves	39	167	333
Writeoffs	(61)	(414)	(117)
Effect of foreign currency translation	1	(2)	28
Ending balance	341	362	611
Inventories
Parts and raw materials	24,910	23,978
Work-in-process	5,984	6,628
Finished goods	6,075	4,928
Inventory, gross	36,969	35,534
Less reserves	(4,401)	(4,436)
Inventories	32,568	31,098
Provision for excess and obsolete inventory	$ 480	$ 351	$ 432