Consolidated Statements of Financial Condition (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Common stock, par value	$ 1	$ 1
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	5,113,951	5,090,901
Common stock, shares outstanding	5,098,068	5,080,857
Treasury stock, shares	15,883	10,044