Note 7 - Geographic Segment Data - Financial Information by Geographic Area (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Sales to outside customers	$ 15,984,726	$ 12,811,697	$ 29,963,903	$ 28,171,335
Total Assets	40,743,262		40,743,262		$ 39,984,038
UNITED STATES
Sales to outside customers	12,075,000	9,480,000	21,813,000	21,125,000
Total Assets	27,286,000		27,286,000		27,784,000
Europe [Member]
Sales to outside customers	1,275,000	917,000	2,637,000	1,864,000
Total Assets	2,901,000		2,901,000		2,989,000
MEXICO
Sales to outside customers	2,378,000	1,956,000	4,564,000	3,979,000
Total Assets	9,473,000		9,473,000		8,288,000
UNITED KINGDOM
Sales to outside customers	257,000	$ 459,000	950,000	$ 1,203,000
Total Assets	$ 1,083,000		$ 1,083,000		$ 923,000