Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Statement of Financial Position [Abstract]
Held-to-Maturity Securities, at Fair Value	$ 282,719	$ 335,901	$ 343,899
Preferred Stock, par value, in dollars per share	$ 5	$ 5	$ 5
Preferred Stock, shares authorized	1,000,000	1,000,000	1,000,000
Common Stock, par value, in dollars per share	$ 1	$ 1	$ 1
Common Stock, shares authorized	20,000,000	20,000,000	20,000,000
Common Stock, shares issued	19,035,565	18,481,301	18,481,301
Unallocated ESOP Shares, in shares	9,932	9,643	20,050
Treasury Stock, in shares	4,584,147	4,541,524	4,570,291