Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 10	$ 10
Preferred stock, shares authorized	500,000	500,000
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized	10,000,000	10,000,000
Common stock, shares issued	3,416,013	3,430,103
Common stock, unvested restricted shares	27,078	18,488