Inventories (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Inventories
Raw materials	$ 29,379,000	$ 23,554,000
Work in process	25,281,000	20,135,000
Finished goods	2,378,000	2,151,000
Inventories, total	57,038,000	45,840,000
Inventory reserve	13,700,000	13,300,000
Excess and obsolete inventory	$ 26,000	$ 291,000