QUARTERLY FINANCIAL INFORMATION (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Net sales	$ 163,539	$ 155,043	$ 163,687	$ 161,410	$ 159,264	$ 150,716	$ 147,082	$ 137,728	$ 643,679	$ 594,790	$ 553,204
Gross profit	51,325	48,002	53,466	51,459	51,638	46,181	46,761	44,429	204,252	189,009	180,861
Earnings before income taxes	25,263	23,529	25,061	25,177	24,522	20,697	22,560	20,710	99,030	88,488	82,934
Net earnings	$ 20,334	$ 19,214	$ 19,679	$ 19,346	$ 41,975	$ 16,043	$ 16,536	$ 15,518	$ 78,573	$ 90,071	$ 55,972
Basic net earnings per common share (in dollars per share)	$ 0.63	$ 0.60	$ 0.61	$ 0.60	$ 1.31	$ 0.50	$ 0.52	$ 0.49	$ 2.45	$ 2.83	$ 1.78
Diluted net earnings per common share (in dollars per share)	$ 0.63	$ 0.59	$ 0.61	$ 0.60	$ 1.30	$ 0.50	$ 0.51	$ 0.48	$ 2.42	$ 2.79	$ 1.75