Investment Securities (Available-for-sale Securities) (Details) - USD ($)	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities
Securities of a single issuer, other than US Treasury, government agencies and US government sponsored agencies exceeding 10% of Stockholders' Equity	$ 0
Amortized Cost	785,544,000	$ 780,304,000
Gross Unrealized Gains	20,001,000	13,196,000
Gross Unrealized Losses	(3,351,000)	(8,799,000)
Available-for-sale securities	802,194,000	784,701,000
U.S. government sponsored agencies
Schedule of Available-for-sale Securities
Amortized Cost	1,944,000	2,908,000
Gross Unrealized Gains	60,000	58,000
Gross Unrealized Losses	0	0
Available-for-sale securities	2,004,000	2,966,000
States and political subdivisions
Schedule of Available-for-sale Securities
Amortized Cost	110,139,000	111,283,000
Gross Unrealized Gains	4,192,000	3,487,000
Gross Unrealized Losses	(3,000)	(44,000)
Available-for-sale securities	114,328,000	114,726,000
Residential mortgage-backed securities
Schedule of Available-for-sale Securities
Amortized Cost	642,835,000	635,504,000
Gross Unrealized Gains	10,293,000	4,905,000
Gross Unrealized Losses	(2,454,000)	(8,116,000)
Available-for-sale securities	650,674,000	632,293,000
Commercial mortgage-backed securities
Schedule of Available-for-sale Securities
Amortized Cost	23,668,000	23,770,000
Gross Unrealized Gains	590,000	119,000
Gross Unrealized Losses	0	(44,000)
Available-for-sale securities	24,258,000	23,845,000
Bank-issued trust preferred securities
Schedule of Available-for-sale Securities
Amortized Cost	5,152,000	5,146,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(822,000)	(511,000)
Available-for-sale securities	4,330,000	4,635,000
Equity securities
Schedule of Available-for-sale Securities
Amortized Cost	1,806,000	1,693,000
Gross Unrealized Gains	4,866,000	4,627,000
Gross Unrealized Losses	(72,000)	(84,000)
Available-for-sale securities	$ 6,600,000	$ 6,236,000