Property, Plant & Equipment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant & Equipment:
Property, plant and equipment	$ 144,849,000	$ 140,658,000
Accumulated depreciation	(76,218,000)	(70,057,000)
Property, plant and equipment — net	68,631,000	70,601,000
Commitments for capital expenditures in progress recorded on balance sheet	1,071,000	616,000
Capital Expenditures Incurred but Not yet Paid	278,000	316,000	$ 464,000
Capitalized interest expense	7,000	0
Land and land improvements
Property, Plant & Equipment:
Property, plant and equipment	6,009,000	5,958,000
Buildings
Property, Plant & Equipment:
Property, plant and equipment	42,769,000	42,593,000
Machinery and equipment
Property, Plant & Equipment:
Property, plant and equipment	92,218,000	89,692,000
Tools, dies and patterns
Property, Plant & Equipment:
Property, plant and equipment	808,000	808,000
Asset under Construction [Member]
Property, Plant & Equipment:
Property, plant and equipment	$ 3,045,000	$ 1,607,000