Inventories - Summary of inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
Raw material and common parts, net of reserve	$ 7,618	$ 6,627
Work-in-process	2,062	2,699
Finished goods, net of reserve	3,613	3,161
Total inventories	$ 13,293	$ 12,487