Segment Information - Financial Data by Segment (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Net sales	$ 31,130,000	$ 34,731,000	$ 39,751,000	$ 31,709,000	$ 30,171,000	$ 33,785,000	$ 38,849,000	$ 27,745,000	$ 137,321,395	$ 130,550,349
Operating income									7,456,906	7,883,053
Assets	109,477,786				114,729,806				109,477,786	114,729,806
Additions to property, plant and equipment									2,851,000	7,146,000
Depreciation and amortization									3,229,000	2,895,000
United States
Net sales									120,993,000	115,407,000
Operating income									6,103,000	6,788,000
Assets	99,720,000				104,431,000				99,720,000	104,431,000
Additions to property, plant and equipment									2,705,000	7,014,000
Depreciation and amortization									3,153,000	2,845,000
Canada
Net sales									7,040,000	6,935,000
Operating income									884,000	775,000
Assets	3,839,000				4,926,000				3,839,000	4,926,000
Additions to property, plant and equipment									83,000	19,000
Depreciation and amortization									9,000	8,000
Europe
Net sales									9,288,000	8,208,000
Operating income									470,000	320,000
Assets	$ 5,918,000				$ 5,373,000				5,918,000	5,373,000
Additions to property, plant and equipment									63,000	113,000
Depreciation and amortization									$ 67,000	$ 42,000