Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Loans, allowance for loan losses	$ 7,287	$ 7,770	[1]
Common stock, par value	$ 5	$ 5	[1]
Common stock, authorized shares	30,000,000	30,000,000	[1]
Common stock, outstanding shares	13,238,716	13,203,605	[1]
Preferred stock, outstanding shares	0	0

[1] Derived from audited December 31, 2017 Consolidated Financial Statements.