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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Total net sales	$ 28,389	$ 24,165	$ 27,020	$ 25,994	$ 26,153	$ 24,822	$ 25,753	$ 24,139	$ 105,568	$ 100,867	$ 89,151
Gross profit	19,218	17,255	18,992	18,474	18,251	17,577	17,516	17,353	73,939	70,697	62,936
Income (loss) from operations	7,193	4,613	11,541	4,862	6,321	5,053	5,536	4,193	28,209	21,103	16,336
Net income	$ 6,025	$ 4,314	$ 8,751	$ 3,853	$ 4,284	$ 5,042	$ 4,632	$ 3,219	$ 22,943	$ 17,177	$ 10,590
Basic:
Basic (in dollars per share)	$ 0.31	$ 0.22	$ 0.45	$ 0.20	$ 0.22	$ 0.26	$ 0.25	$ 0.17	$ 1.18	$ 0.91	$ 0.57
Diluted (in dollars per share)	$ 0.30	$ 0.21	$ 0.43	$ 0.19	$ 0.21	$ 0.25	$ 0.23	$ 0.16	$ 1.13	$ 0.86	$ 0.55
Total net sales	$ 28,389	$ 24,165	$ 27,020	$ 25,994	$ 26,153	$ 24,822	$ 25,753	$ 24,139	$ 105,568	$ 100,867	$ 89,151
Gross profit	19,218	17,255	18,992	18,474	18,251	17,577	17,516	17,353	73,939	70,697	62,936
Income (loss) from operations	7,193	4,613	11,541	4,862	6,321	5,053	5,536	4,193	28,209	21,103	16,336
Net income	$ 6,025	$ 4,314	$ 8,751	$ 3,853	$ 4,284	$ 5,042	$ 4,632	$ 3,219	$ 22,943	$ 17,177	$ 10,590