Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Accounts receivable, less allowances	$ 3,436	$ 3,464
Common stock, par value	$ 2	$ 2
Common stock, shares authorized	15,000,000	15,000,000
Common stock, shares issued	4,912,959	4,902,233
Common stock, shares outstanding	4,912,959	4,902,233
Common stock, shares issued to rabbi trust	261,781	265,508
Treasury stock shares	1,664,517	1,611,927