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
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 100,915	$ 102,964	$ 92,560	$ 99,082	$ 92,463	$ 90,685	$ 90,501	$ 89,096	$ 395,521	$ 362,745	$ 376,089
Cost of sales	69,184	79,802	71,858	75,871	70,903	71,895	70,979	72,436	296,715	286,213	292,490
Gross profit	31,731	23,162	20,702	23,211	21,560	18,790	19,522	16,660	98,806	76,532	83,599
SG&A expenses	16,188	9,510	9,364	9,503	5,309	7,186	8,648	8,147	44,565	29,290	33,451
Operating income	15,543	13,652	11,338	13,708	16,251	11,604	10,874	8,513	54,241	47,242	50,148
Interest expense, net and other	(291)	(409)	(298)	(642)	(368)	(364)	(321)	(252)	(1,640)	(1,305)	(1,168)
Income before income taxes	15,252	13,243	11,040	13,066	15,883	11,240	10,553	8,261	52,601	45,937	48,980
Income tax expense (benefit)	3,620	2,862	2,550	3,224	2,936	3,025	2,642	(1,459)	12,256	7,144	11,696
Net income	$ 11,632	$ 10,381	$ 8,490	$ 9,842	$ 12,947	$ 8,215	$ 7,911	$ 9,720	$ 40,345	$ 38,793	$ 37,284
Basic and diluted EPS data (in dollars per share)	$ 0.69	$ 0.61	$ 0.50	$ 0.57	$ 0.76	$ 0.48	$ 0.46	$ 0.57	$ 2.37	$ 2.27	$ 2.17