Securities (Summary of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available for Sale and Held to Maturity Securities [Line Items]
Available for sale securities amortized cost	$ 790,801	$ 750,745
Available for sale securities unrealized gains	3,688	5,008
Available for sale securities unrealized losses	(13,535)	(15,841)
Available for sale, at fair value	780,954	739,912
Held to maturity securities amortized cost	12,541	15,633
Held to maturity securities unrealized gains	180	287
Held to Matruity securities unrealized losses	0	0
Held to maturity securities fair value	12,721	15,920
Total securities amortized cost	803,342	766,378
Total securities unrealized gains	3,868	5,295
Total securities unrealized losses	(13,535)	(15,841)
Total securities fair value	793,675	755,832
Available for sale securities amortized cost	790,801
Obligations of U.S. government-sponsored enterprises [Member]
Schedule of Available for Sale and Held to Maturity Securities [Line Items]
Available for sale securities amortized cost	161,479	111,483
Available for sale securities unrealized gains	0	7
Available for sale securities unrealized losses	(3,875)	(3,050)
Available for sale, at fair value	157,604	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 Maturity Securities [Line Items]
Available for sale securities amortized cost	594,944	592,833
Available for sale securities unrealized gains	3,671	4,923
Available for sale securities unrealized losses	(7,733)	(9,671)
Available for sale, at fair value	590,882	588,085
Held to maturity securities amortized cost	12,541	15,633
Held to maturity securities unrealized gains	180	287
Held to Matruity securities unrealized losses	0	0
Held to maturity securities fair value	12,721	15,920
Obligations of states and political subdivisions [Member]
Schedule of Available for Sale and Held to Maturity Securities [Line Items]
Available for sale securities amortized cost	2,355	14,423
Available for sale securities unrealized gains	4	62
Available for sale securities unrealized losses	0	0
Available for sale, at fair value	2,359	14,485
Individual name issuer trust preferred debt securities [Member]
Schedule of Available for Sale and Held to Maturity Securities [Line Items]
Available for sale securities amortized cost	18,106	29,851
Available for sale securities unrealized gains	0	0
Available for sale securities unrealized losses	(1,122)	(3,115)
Available for sale, at fair value	16,984	26,736
Corporate bonds [Member]
Schedule of Available for Sale and Held to Maturity Securities [Line Items]
Available for sale securities amortized cost	13,917	2,155
Available for sale securities unrealized gains	13	16
Available for sale securities unrealized losses	(805)	(5)
Available for sale, at fair value	$ 13,125	$ 2,166

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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