Note 14 - Quarterly Financial Data (Unaudited) - Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total net sales	$ 30,170	$ 29,100	$ 29,483	$ 28,479	$ 28,389	$ 24,165	$ 27,020	$ 25,994	$ 117,232	$ 105,568	$ 100,867
Gross profit	19,908	20,166	20,315	19,464	19,218	17,255	18,992	18,474	79,853	73,939	70,697
Income (loss) from operations	4,928	5,905	5,915	4,435	7,193	4,613	11,541	4,862	21,183	28,209	21,103
Net income	$ 4,613	$ 5,184	$ 4,624	$ 3,513	$ 6,025	$ 4,314	$ 8,751	$ 3,853	$ 17,934	$ 22,943	$ 17,177
Basic:
Basic (in dollars per share)	$ 0.23	$ 0.26	$ 0.23	$ 0.18	$ 0.31	$ 0.22	$ 0.45	$ 0.20	$ 0.91	$ 1.18	$ 0.91
Diluted (in dollars per share)	$ 0.23	$ 0.25	$ 0.23	$ 0.17	$ 0.30	$ 0.21	$ 0.43	$ 0.19	$ 0.88	$ 1.13	$ 0.86
Total net sales	$ 30,170	$ 29,100	$ 29,483	$ 28,479	$ 28,389	$ 24,165	$ 27,020	$ 25,994	$ 117,232	$ 105,568	$ 100,867
Gross profit	19,908	20,166	20,315	19,464	19,218	17,255	18,992	18,474	79,853	73,939	70,697
Income (loss) from operations	4,928	5,905	5,915	4,435	7,193	4,613	11,541	4,862	21,183	28,209	21,103
Net income	$ 4,613	$ 5,184	$ 4,624	$ 3,513	$ 6,025	$ 4,314	$ 8,751	$ 3,853	$ 17,934	$ 22,943	$ 17,177