Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Receivables, allowance for doubtful accounts	$ 962	$ 2,228
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	20,000,000	20,000,000
Common stock, shares issued	12,361,000	12,271,000
Common stock, shares outstanding	12,361,000	12,271,000