CONDENSED CONSOLIDATED STATEMENTS OF CONDITION (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Available-for-sale securities, at amortized cost	$ 1,360,508	$ 1,408,996
Held-to-maturity securities, at fair value	138,232	140,315
Equity Securities, at amortized cost	$ 1,000	$ 1,000
Common Stock, par value (in dollars per share)	$ 0.1	$ 0.1
Common Stock, authorized (in shares)	25,000,000	25,000,000
Common Stock, issued (in shares)	15,313,825	15,301,524
Treasury stock, shares (in shares)	120,278	120,805