Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Securities held-to-maturity, Estimated Fair Value	$ 59,628	$ 65,646
Preferred stock, par value (in dollars per share)	$ 25	$ 25
Preferred stock, shares authorized (in shares)	500,000	500,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	50,000,000	50,000,000
Common stock, shares issued (in shares)	19,047,548	19,047,548
Common stock, treasury shares (in shares)	3,595,092	3,429,519