Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Accounts receivable, less allowances	$ 3,289	$ 3,325
Common stock, par value	$ 2	$ 2
Common stock, shares authorized	15,000,000	15,000,000
Common stock, shares issued	5,012,109	5,038,207
Common stock, shares outstanding	5,012,109	5,038,207
Common stock, shares issued to rabbi trust	269,630	289,026
Treasury stock shares	1,309,617	1,258,069