Securities (Summary of Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	$ 811,302	$ 790,801
Available for sale securities unrealized gains	1,949	3,688
Available for sale securities unrealized losses	(25,409)	(13,535)
Available for sale, at fair value	787,842	780,954
Held to maturity securities	11,973	12,541
Held to maturity securities unrealized gains	38	180
Held to maturity securities unrealized losses	(16)	0
Held to maturity securities fair value	11,995	12,721
Total available for sale and held to maturity securities amortized cost	823,275	803,342
Total available for sale and held to maturity securities unrealized gains	1,987	3,868
Total available for sale and held to maturity securities unrealized losses	(25,425)	(13,535)
Total available for sale and held to maturity securities fair value	799,837	793,675
Obligations of U.S. government-sponsored enterprises [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	171,491	161,479
Available for sale securities unrealized gains	9	0
Available for sale securities unrealized losses	(5,886)	(3,875)
Available for sale, at fair value	165,614	157,604
Mortgage-backed securities issued by U.S. government-sponsored agencies and U.S. government-sponsored enterprises [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	605,430	594,944
Available for sale securities unrealized gains	1,936	3,671
Available for sale securities unrealized losses	(17,619)	(7,733)
Available for sale, at fair value	589,747	590,882
Held to maturity securities	11,973	12,541
Held to maturity securities unrealized gains	38	180
Held to maturity securities unrealized losses	(16)	0
Held to maturity securities fair value	11,995	12,721
Obligations of states and political subdivisions [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	2,355	2,355
Available for sale securities unrealized gains	4	4
Available for sale securities unrealized losses	0	0
Available for sale, at fair value	2,359	2,359
Individual name issuer trust preferred debt securities
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	18,112	18,106
Available for sale securities unrealized gains	0	0
Available for sale securities unrealized losses	(1,016)	(1,122)
Available for sale, at fair value	17,096	16,984
Corporate bonds [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	13,914	13,917
Available for sale securities unrealized gains	0	13
Available for sale securities unrealized losses	(888)	(805)
Available for sale, at fair value	$ 13,026	$ 13,125

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

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