Note 7 - Segment Information - Summary of Reportable Operating Segments (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Net sales	$ 19,177,767	$ 19,280,770	$ 39,466,685	$ 39,430,615
Gross profit	13,118,442	12,895,534	25,961,404	25,181,579
Operating income (loss)	1,981,481	1,655,437	3,750,442	3,392,928
Interest (expense)	(78,182)	(53,680)	(142,824)	(90,024)
Other income (expense), net	46,741	17,012	85,613	19,663
Income (loss) before income taxes	1,950,040	1,618,769	3,693,231	3,322,567
Depreciation and amortization	413,433	471,290	878,955	929,408
Fixed asset additions	181,841	405,149	421,861	1,004,906
Total assets	75,785,223	72,243,459	75,785,223	72,243,459	$ 74,914,596
North America Segment [Member]
Net sales	18,276,885	18,427,425	37,594,145	37,659,139
Gross profit	12,519,089	12,449,202	24,745,091	24,202,159
Operating income (loss)	1,986,190	1,814,887	3,816,849	3,626,450
Interest (expense)	(78,182)	(53,680)	(142,824)	(90,024)
Other income (expense), net	38,343	15,195	73,527	32,849
Income (loss) before income taxes	1,946,351	1,776,402	3,747,552	3,569,275
Depreciation and amortization	387,700	448,788	829,252	885,069
Fixed asset additions	105,422	387,054	343,080	984,880
Total assets	71,184,080	67,412,189	71,184,080	67,412,189
International [Member]
Net sales	900,882	853,345	1,872,540	1,771,476
Gross profit	599,353	446,332	1,216,313	979,420
Operating income (loss)	(4,709)	(159,450)	(66,407)	(233,522)
Interest (expense)
Other income (expense), net	8,398	1,817	12,086	(13,186)
Income (loss) before income taxes	3,689	(157,633)	(54,321)	(246,708)
Depreciation and amortization	25,733	22,502	49,703	44,339
Fixed asset additions	76,419	18,095	78,781	20,026
Total assets	$ 4,601,143	$ 4,831,270	$ 4,601,143	$ 4,831,270