Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Accounts receivable, less allowances	$ 3,210	$ 2,326
Common stock, par value	$ 2	$ 2
Common stock, shares authorized	15,000,000	15,000,000
Common stock, shares issued	5,117,753	5,221,062
Common stock, shares outstanding	5,117,753	5,221,062
Common stock, shares issued to rabbi trust	297,281	296,635
Treasury stock shares	1,136,443	1,018,013