Investment Securities (Details) $ in Thousands	3 Months Ended
Mar. 31, 2018 USD ($) securities	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Available-for-sale: [Abstract]
Amortized Cost	$ 581,607		$ 581,543
Gross Unrealized Gains	1,259		2,900
Gross Unrealized (Losses)	(13,004)		(5,864)
Fair Value	569,862		578,579
Gain (Loss) on Sale of Securities, Net	20	$ 0
Held-to-maturity: [Abstract]
Held-to-maturity Securities	69,358		69,332
Held-to-maturity Securities, Fair Value	67,631		68,457
Realized Investment Gains (Losses) [Abstract]
Gross gains	20	0
Gross losses	0	$ 0
U.S. Treasury securities and obligations of U.S. government corporations & agencies
Available-for-sale: [Abstract]
Amortized Cost	124,819		115,796
Gross Unrealized Gains	0		8
Gross Unrealized (Losses)	(3,734)		(2,034)
Fair Value	121,085		113,770
Held-to-maturity: [Abstract]
Held-to-maturity Securities	69,358		69,332
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	8		103
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(1,735)		(978)
Held-to-maturity Securities, Fair Value	67,631		68,457
Obligations of states and political subdivisions
Available-for-sale: [Abstract]
Amortized Cost	161,424		165,037
Gross Unrealized Gains	1,029		2,254
Gross Unrealized (Losses)	(2,228)		(1,025)
Fair Value	160,225		166,266
Mortgage-backed securities: GSE residential
Available-for-sale: [Abstract]
Amortized Cost	290,477		295,778
Gross Unrealized Gains	75		493
Gross Unrealized (Losses)	(6,715)		(2,460)
Fair Value	283,837		293,811
Trust preferred securities
Available-for-sale: [Abstract]
Amortized Cost	2,849		2,893
Gross Unrealized Gains	0		0
Gross Unrealized (Losses)	(327)		(345)
Fair Value	$ 2,522		2,548
Number of trust preferred securities \| securities	1
Trust preferred securities \| Maximum [Member]
Available-for-sale: [Abstract]
Maturities of Debt Securities	twenty years
Other securities
Available-for-sale: [Abstract]
Amortized Cost	$ 2,038		2,039
Gross Unrealized Gains	155		145
Gross Unrealized (Losses)	0		0
Fair Value	$ 2,193		$ 2,184

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Amount of investments in debt securities classified as available-for-sale, expected to be converted to cash, sold or exchanged within one year or the normal operating cycle, if longer.

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