QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (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, 2017	Dec. 31, 2016	Dec. 31, 2015
QUARTERLY FINANCIAL INFORMATION (UNAUDITED) [Abstract]
Net sales	$ 159,264	$ 150,716	$ 147,082	$ 137,728	$ 140,760	$ 138,509	$ 138,794	$ 135,141	$ 594,790	$ 553,204	$ 552,492
Gross profit	51,638	46,181	46,761	44,429	46,932	44,656	46,449	42,824	189,009	180,861	168,097
Earnings before income taxes	24,522	20,697	22,560	20,710	22,799	20,771	21,383	17,981	88,488	82,934	87,063
Net earnings	$ 41,975	$ 16,043	$ 16,536	$ 15,518	$ 15,924	$ 14,012	$ 14,150	$ 11,886	$ 90,071	$ 55,972	$ 59,722
Basic net earnings per common share (in dollars per share)	$ 1.31	$ 0.50	$ 0.52	$ 0.49	$ 0.51	$ 0.44	$ 0.45	$ 0.38	$ 2.83	$ 1.78	$ 1.92
Diluted net earnings per common share (in dollars per share)	$ 1.30	$ 0.50	$ 0.51	$ 0.48	$ 0.50	$ 0.44	$ 0.44	$ 0.37	$ 2.79	$ 1.75	$ 1.89