CONDENSED CONSOLIDATED STATEMENTS OF CONDITION - (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	23,996,293	23,901,084
Common stock, shares outstanding	23,996,293	23,901,084