Inventories (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Inventories:
Raw materials	$ 25,626,000	$ 23,554,000
Work in process	23,805,000	20,135,000
Finished goods	1,691,000	2,151,000
Inventories, total	51,122,000	45,840,000
Inventory reserve	13,700,000	13,300,000
Excess and obsolete inventory	$ 322,000	$ 291,000