Securities (Summary of Amortized Costs and Estimated Fair Values of Available-For-Sale Securities) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	$ 803,021	$ 789,229
Available-for-sale, Unrealized Gains	1,139	3,174
Available-for-sale, Unrealized Losses	(14,261)	(12,536)
AFS securities	789,899	779,867
Held-to-maturity Securities	94,073	94,609
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1,077	618
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(237)	(631)
Held-to-maturity Securities, Fair Value	94,913	94,596
US Government Corporations and Agencies Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities	94,073	94,609
Held-to-maturity Securities, Accumulated Unrecognized Holding Gain	1,077	618
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	(237)	(631)
Held-to-maturity Securities, Fair Value	94,913	94,596
Obligations of states and political subdivisions [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	7,232	8,848
Available-for-sale, Unrealized Gains	103	153
Available-for-sale, Unrealized Losses	0	0
AFS securities	7,335	9,001
Mortgage-backed securities issued or guaranteed by U.S. government sponsored enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	510,176	485,222
Available-for-sale, Unrealized Gains	597	2,515
Available-for-sale, Unrealized Losses	(7,471)	(7,115)
AFS securities	503,302	480,622
Collateralized mortgage obligations issued or guaranteed by U.S. government sponsored enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	279,575	289,046
Available-for-sale, Unrealized Gains	14	265
Available-for-sale, Unrealized Losses	(6,790)	(5,421)
AFS securities	272,799	283,890
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	5,484	5,481
Available-for-sale, Unrealized Gains	173	132
Available-for-sale, Unrealized Losses	0	0
AFS securities	5,657	5,613
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	802,467	788,597
Available-for-sale, Unrealized Gains	887	3,065
Available-for-sale, Unrealized Losses	(14,261)	(12,536)
AFS securities	789,093	779,126
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale, Amortized Cost	554	632
Available-for-sale, Unrealized Gains	252	109
Available-for-sale, Unrealized Losses	0	0
AFS securities	$ 806	$ 741

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

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-Publisher FASB
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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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