Note 7 - Segment Information - Summary of Reportable Operating Segments (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Net sales	$ 18,887,099	$ 18,388,381	$ 58,353,784	$ 57,818,996
Gross profit	11,846,833	11,635,331	37,808,237	36,816,910
Operating income (loss)	315,444	650,275	4,065,886	4,043,203
Interest (expense)	(80,710)	(53,141)	(223,534)	(143,165)
Other income (expense), net	40,846	95,936	126,459	115,599
Income (loss) before income taxes	275,580	693,070	3,968,811	4,015,637
Depreciation and amortization	431,789	537,126	1,310,774	1,466,534
Fixed asset additions	465,817	525,641	887,679	1,530,547
Total assets	76,665,750	74,371,841	76,665,750	74,371,841	$ 74,914,596
North America Segment [Member]
Net sales	18,046,045	17,421,013	55,640,190	55,080,152
Gross profit	11,383,738	11,037,486	36,128,829	35,239,645
Operating income (loss)	566,544	649,797	4,383,393	4,276,247
Interest (expense)	(80,710)	(53,141)	(223,534)	(143,165)
Other income (expense), net	34,583	94,196	108,110	127,045
Income (loss) before income taxes	520,417	690,852	4,267,969	4,260,127
Depreciation and amortization	407,841	513,250	1,237,093	1,398,319
Fixed asset additions	437,615	523,546	780,696	1,508,426
Total assets	72,009,096	70,083,363	72,009,096	70,083,363
International [Member]
Net sales	841,054	967,368	2,713,594	2,738,844
Gross profit	463,095	597,845	1,679,408	1,577,265
Operating income (loss)	(251,100)	478	(317,507)	(233,044)
Interest (expense)
Other income (expense), net	6,263	1,740	18,349	(11,446)
Income (loss) before income taxes	(244,837)	2,218	(299,158)	(244,490)
Depreciation and amortization	23,948	23,876	73,651	68,215
Fixed asset additions	28,202	2,095	106,983	22,121
Total assets	$ 4,656,654	$ 4,288,478	$ 4,656,654	$ 4,288,478