Securities (Summary of Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	$ 764,917	$ 750,745
Available for sale securities unrealized gains	4,915	5,008
Available for sale securities unrealized losses	(15,112)	(15,841)
Available for sale, at fair value	754,720	739,912
Held to maturity securities	14,721	15,633
Held to maturity securities unrealized gains	244	287
Held to maturity securities unrealized losses	0	0
Held to maturity securities fair value	14,965	15,920
Total available for sale and held to maturity securities amortized cost	779,638	766,378
Total available for sale and held to maturity securities unrealized gains	5,159	5,295
Total available for sale and held to maturity securities unrealized losses	(15,112)	(15,841)
Total available for sale and held to maturity securities fair value	769,685	755,832
Obligations of U.S. government 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	131,456	111,483
Available for sale securities unrealized gains	28	7
Available for sale securities unrealized losses	(3,240)	(3,050)
Available for sale, at fair value	128,244	108,440
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	592,902	592,833
Available for sale securities unrealized gains	4,837	4,923
Available for sale securities unrealized losses	(8,946)	(9,671)
Available for sale, at fair value	588,793	588,085
Held to maturity securities	14,721	15,633
Held to maturity securities unrealized gains	244	287
Held to maturity securities unrealized losses	0	0
Held to maturity securities fair value	14,965	15,920
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	8,548	14,423
Available for sale securities unrealized gains	36	62
Available for sale securities unrealized losses	0	0
Available for sale, at fair value	8,584	14,485
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	27,880	29,851
Available for sale securities unrealized gains	0	0
Available for sale securities unrealized losses	(2,743)	(3,115)
Available for sale, at fair value	25,137	26,736
Corporate bonds [Member]
Schedule of Available for Sale and Held to Maturty Securities [Line Items]
Available for sale securities amortized cost basis	4,131	2,155
Available for sale securities unrealized gains	14	16
Available for sale securities unrealized losses	(183)	(5)
Available for sale, at fair value	$ 3,962	$ 2,166

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

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