Inventories - Summary of inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw material and common parts, net of reserve	$ 7,930	$ 7,618
Work-in-process	3,123	2,062
Finished goods, net of reserve	1,940	3,613
Total inventories	$ 12,993	$ 13,293