Inventories (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Inventory, Net, Items Net of Reserve Alternative [Abstract]
Finished goods	$ 10,129	$ 9,535
Work in process	649	766
Component parts	5,772	5,480
Service parts	5,844	5,965
Inventories-net	22,394	21,746
Inventory reserves	$ 10,700	$ 10,000