Note 17 - Quarterly Results of Operations - Quarterly Financial Information (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
Net sales	$ 87,618	$ 77,785	$ 56,186	$ 55,720	$ 75,341	$ 67,179	$ 61,959	$ 65,929	$ 277,309	$ 270,408
Gross margin	36,121	29,832	19,462	19,320	28,252	25,014	21,441	22,978	104,735	97,685
Net income	9,721	7,613	2,442	1,188	5,085	5,616	3,156	3,605	20,964	17,462
Dividends paid	$ 1,017	$ 1,023	$ 1,023	$ 1,030	$ 1,029	$ 1,036	$ 1,035	$ 887	$ 4,093	$ 3,987
Basic (in dollars per share)	$ 1.34	$ 1.04	$ 0.33	$ 0.16	$ 0.68	$ 0.76	$ 0.43	$ 0.49	$ 2.87	$ 2.36
Diluted (in dollars per share)	$ 1.33	$ 1.04	$ 0.33	$ 0.16	$ 0.70	$ 0.75	$ 0.42	$ 0.48	$ 2.86	$ 2.35