Note 9 - Quarterly Results for 2015, 2016 and 2017 (Unaudited) - Quarterly Results (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net sales	$ 72,450	$ 67,773	$ 65,604	$ 60,987	$ 64,686	$ 65,282	$ 64,660	$ 57,968	$ 53,192	$ 56,662	$ 54,116	$ 46,347
Gross profit	25,975	24,789	23,374	22,214	22,058	23,140	21,763	20,021	17,882	19,224	18,531	15,796	$ 96,352	$ 86,982	$ 71,433
Income before taxes on income	6,834	6,842	5,701	5,405	5,867	6,006	4,615	3,410	4,698	5,581	5,394	3,223
Net earnings used in the computation of basic and diluted earnings per share (in thousands)	$ 1,884	$ 4,962	$ 4,341	$ 3,835	$ 4,441	$ 4,447	$ 3,308	$ 2,442	$ 3,368	$ 4,031	$ 3,624	$ 2,043	$ 15,022	$ 14,638	$ 13,066
Weighted average number of shares outstanding during the period
Net earnings (in dollars per share)	$ 0.13	$ 0.34	$ 0.30	$ 0.27	$ 0.31	$ 0.31	$ 0.23	$ 0.18	$ 0.24	$ 0.29	$ 0.26	$ 0.15	$ 1.04	$ 1.04	$ 0.95
Net earnings (in dollars per share)	$ 0.12	$ 0.33	$ 0.29	$ 0.26	$ 0.30	$ 0.30	$ 0.22	$ 0.17	$ 0.23	$ 0.28	$ 0.25	$ 0.14	$ 0.99	$ 0.98	$ 0.90
(Basic) (in shares)	14,614,691	14,573,813	14,501,399	14,350,721	14,162,939	14,118,354	14,120,617	13,927,063	13,894,907	13,833,561	13,730,646	13,584,922	14,510,156	14,082,243	13,761,009
(Diluted) (in shares)	15,275,222	15,229,722	15,040,431	14,929,695	14,979,746	14,984,084	14,957,469	14,668,658	14,603,464	14,585,688	14,577,342	14,548,084	15,118,768	14,897,489	14,578,644
Net sales	$ 72,450	$ 67,773	$ 65,604	$ 60,987	$ 64,686	$ 65,282	$ 64,660	$ 57,968	$ 53,192	$ 56,662	$ 54,116	$ 46,347
Gross profit	25,975	24,789	23,374	22,214	22,058	23,140	21,763	20,021	17,882	19,224	18,531	15,796	$ 96,352	$ 86,982	$ 71,433
Income before taxes on income	6,834	6,842	5,701	5,405	5,867	6,006	4,615	3,410	4,698	5,581	5,394	3,223
Net earnings used in the computation of basic and diluted earnings per share (in thousands)	$ 1,884	$ 4,962	$ 4,341	$ 3,835	$ 4,441	$ 4,447	$ 3,308	$ 2,442	$ 3,368	$ 4,031	$ 3,624	$ 2,043	$ 15,022	$ 14,638	$ 13,066