Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2015	Dec. 31, 2014
Statement Of Financial Position [Abstract]
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	30,000,000	30,000,000
Common stock, shares issued	25,688,794	25,640,090
Treasury stock, shares	3,428,541	3,384,443