Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Securities held-to-maturity	$ 65,646	$ 76,445
Preferred stock, par value	$ 25	$ 25
Preferred stock, shares authorized	500,000	500,000
Preferred stock, shares issued	0	0
Common stock, par value	$ 2.50	$ 2.50
Common stock, shares authorized	50,000,000	50,000,000
Common stock, shares issued	19,047,548	18,606,944
Common stock, treasury shares	3,429,519	3,478,511