Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Receivables, allowance for doubtful accounts	$ 979	$ 962
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	12,362,000	12,361,000
Common stock, shares outstanding	12,362,000	12,361,000