Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	60,000,000	60,000,000
Common stock, shares issued	25,970,037	25,894,782
Treasury stock, shares	3,501,313	3,470,084