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 (UNAUDITED)
Net Sales	$ 178,337	$ 168,366	$ 128,529	$ 176,054	$ 203,140	$ 195,467	$ 222,346	$ 197,213	$ 651,286	$ 818,166	$ 711,706
Operating Income	14,808	8,612	7,660	7,564	15,174	11,293	14,245	12,382
Net Income	$ 12,020	$ 6,553	$ 5,826	$ 5,431	$ 11,692	$ 8,076	$ 10,683	$ 8,660	$ 29,830	$ 39,111	$ 33,746
Basic Income Per Share (in dollars per share)	$ 1.05	$ 0.57	$ 0.51	$ 0.48	$ 1.03	$ 0.71	$ 0.94	$ 0.76	$ 2.62	$ 3.43	$ 2.96
Diluted Income Per Share (in dollars per share)	1.05	0.57	0.51	0.48	1.03	0.71	0.94	0.76	2.62	3.43	2.96
Cash Dividends Declared Per Share (in dollars per share)	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.18	$ 0.72	$ 0.72	$ 0.72