Note 18 - Quarterly Data (Unaudited) - Summary of Quarterly Data (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Sales	$ 19,933,941	$ 21,277,797	$ 18,576,588	$ 25,281,574	$ 21,103,124	$ 22,244,681	$ 24,514,636	$ 21,836,087	$ 85,069,900	$ 89,698,527
Gross Profit	4,371,691	4,852,417	3,499,039	6,208,143	4,530,251	4,987,563	5,226,933	4,829,888	18,931,290	19,574,635
Operating Income	1,657,368	2,126,417	530,520	3,138,149	2,589,263	2,558,779	2,791,553	2,571,071	7,452,453	10,510,666
Net Income	$ 2,108,890	$ 1,426,090	$ 228,837	$ 2,075,570	$ 1,708,058	$ 1,694,868	$ 1,831,479	$ 1,745,458	$ 5,839,387	$ 6,979,863
Net Income Per Common Share - Basic (in dollars per share)	$ 0.63	$ 0.43	$ 0.07	$ 0.63	$ 0.58	$ 0.59	$ 0.66	$ 0.63	$ 1.76	$ 2.45
Net Income Per Common Share - Diluted (in dollars per share)	$ 0.63	$ 0.43	$ 0.07	$ 0.63	$ 0.51	$ 0.52	$ 0.57	$ 0.55	$ 1.76	$ 2.13