Securities (Summary of Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	$ 804,221	$ 790,801
Available for sale securities unrealized gains	1,648	3,688
Available for sale securities unrealized losses	(29,176)	(13,535)
Available for sale, at fair value	776,693	780,954
Held to maturity securities	11,412	12,541
Held to maturity securities unrealized gains	0	180
Held to maturity securities unrealized losses	(48)	0
Held to maturity securities fair value	11,364	12,721
Total available for sale and held to maturity securities amortized cost	815,633	803,342
Total available for sale and held to maturity securities unrealized gains	1,648	3,868
Total available for sale and held to maturity securities unrealized losses	(29,224)	(13,535)
Total available for sale and held to maturity securities fair value	788,057	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	171,496	161,479
Available for sale securities unrealized gains	0	0
Available for sale securities unrealized losses	(6,960)	(3,875)
Available for sale, at fair value	164,536	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	604,578	594,944
Available for sale securities unrealized gains	1,646	3,671
Available for sale securities unrealized losses	(20,540)	(7,733)
Available for sale, at fair value	585,684	590,882
Held to maturity securities	11,412	12,541
Held to maturity securities unrealized gains	0	180
Held to maturity securities unrealized losses	(48)	0
Held to maturity securities fair value	11,364	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	935	2,355
Available for sale securities unrealized gains	2	4
Available for sale securities unrealized losses	0	0
Available for sale, at fair value	937	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	13,299	18,106
Available for sale securities unrealized gains	0	0
Available for sale securities unrealized losses	(799)	(1,122)
Available for sale, at fair value	12,500	16,984
Corporate bonds [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	13,913	13,917
Available for sale securities unrealized gains	0	13
Available for sale securities unrealized losses	(877)	(805)
Available for sale, at fair value	$ 13,036	$ 13,125

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

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