Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Allowances	$ 9,654	$ 10,116
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	60,000,000	60,000,000
Common stock, shares issued	26,308,668	26,070,787
Treasury stock, shares	3,803,043	3,561,509