CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
CURRENT ASSETS:
Accounts receivable, allowances for discounts and expected credit losses	$ 6,660	$ 6,170
Property, plant and equipment, accumulated depreciation	$ 232,112	$ 227,788
Stockholders' equity:
Common stock, par value (in dollars per share)	$ 2.00	$ 2.00
Common stock, shares authorized (in shares)	30,000,000	30,000,000
Common stock, shares issued (in shares)	23,936,036	23,936,036
Treasury stock - at cost (in shares)	2,011,019	1,911,792