Note 15 - Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	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	Dec. 31, 2018
Total net sales	$ 37,548	$ 36,416	$ 24,851	$ 30,551	$ 30,170	$ 29,100	$ 29,483	$ 28,479	$ 129,366	$ 117,232	$ 105,568
Gross profit	24,402	22,704	17,029	20,483	19,908	20,166	20,315	19,464	84,618	79,853	73,939
Income (loss) from operations	9,545	10,018	4,872	4,353	4,928	5,905	5,915	4,435	28,788	21,183	28,209
Net income	$ 7,033	$ 7,513	$ 3,500	$ 3,174	$ 4,613	$ 5,184	$ 4,624	$ 3,513	$ 21,220	$ 17,934	$ 22,943
Basic:
Basic (in dollars per share)	$ 0.35	$ 0.37	$ 0.17	$ 0.16	$ 0.23	$ 0.26	$ 0.23	$ 0.18	$ 1.05	$ 0.91	$ 1.18
Diluted (in dollars per share)	$ 0.34	$ 0.37	$ 0.17	$ 0.16	$ 0.23	$ 0.25	$ 0.23	$ 0.17	$ 1.04	$ 0.88	$ 1.13
Total net sales	$ 37,548	$ 36,416	$ 24,851	$ 30,551	$ 30,170	$ 29,100	$ 29,483	$ 28,479	$ 129,366	$ 117,232	$ 105,568
Gross profit	24,402	22,704	17,029	20,483	19,908	20,166	20,315	19,464	84,618	79,853	73,939
Income (loss) from operations	9,545	10,018	4,872	4,353	4,928	5,905	5,915	4,435	28,788	21,183	28,209
Net income	$ 7,033	$ 7,513	$ 3,500	$ 3,174	$ 4,613	$ 5,184	$ 4,624	$ 3,513	$ 21,220	$ 17,934	$ 22,943