Consolidated Balance Sheet Parenthetical - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Statement of Financial Position [Abstract]
Held-to-Maturity Securities, at Fair Value	$ 324,938	$ 335,901	$ 335,105
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	18,481,301	18,481,301	17,943,201
Unallocated ESOP Shares ,in shares	9,643	9,643	19,466
Treasury Stock, in shares	4,516,444	4,541,524	4,442,292