QUARTERLY FINANCIAL INFORMATION (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]
Net sales	$ 180,713	$ 175,140	$ 173,355	$ 174,436	$ 166,527	$ 158,595	$ 161,554	$ 157,029	$ 703,644	$ 643,705	$ 643,679
Gross margin	56,818	56,368	55,380	55,331	54,346	54,008	53,918	49,095	223,897	211,367	204,252
Earnings before income tax expense	28,047	27,907	25,973	24,490	22,368	24,436	24,881	24,793	106,417	96,478	99,030
Net earnings	$ 22,162	$ 21,568	$ 21,125	$ 19,768	$ 20,383	$ 20,676	$ 19,829	$ 18,783	$ 84,623	$ 79,671	$ 78,573
Basic net earnings per common share (in dollars per share)	$ 0.69	$ 0.67	$ 0.66	$ 0.62	$ 0.64	$ 0.64	$ 0.62	$ 0.58	$ 2.63	$ 2.48	$ 2.45
Diluted net earnings per common share (in dollars per share)	$ 0.68	$ 0.66	$ 0.65	$ 0.61	$ 0.63	$ 0.64	$ 0.61	$ 0.58	$ 2.60	$ 2.45	$ 2.42