Investment Securities (Available-for-sale Securities) (Details) - USD ($)	Sep. 30, 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	743,878,000	$ 780,304,000
Gross Unrealized Gains	20,935,000	13,196,000
Gross Unrealized Losses	(2,670,000)	(8,799,000)
Available-for-sale securities	762,143,000	784,701,000
U.S. government sponsored agencies
Schedule of Available-for-sale Securities
Amortized Cost	998,000	2,908,000
Gross Unrealized Gains	3,000	58,000
Gross Unrealized Losses	0	0
Available-for-sale securities	1,001,000	2,966,000
States and political subdivisions
Schedule of Available-for-sale Securities
Amortized Cost	113,530,000	111,283,000
Gross Unrealized Gains	4,309,000	3,487,000
Gross Unrealized Losses	0	(44,000)
Available-for-sale securities	117,839,000	114,726,000
Residential mortgage-backed securities
Schedule of Available-for-sale Securities
Amortized Cost	599,589,000	635,504,000
Gross Unrealized Gains	10,037,000	4,905,000
Gross Unrealized Losses	(2,174,000)	(8,116,000)
Available-for-sale securities	607,452,000	632,293,000
Commercial mortgage-backed securities
Schedule of Available-for-sale Securities
Amortized Cost	22,658,000	23,770,000
Gross Unrealized Gains	625,000	119,000
Gross Unrealized Losses	0	(44,000)
Available-for-sale securities	23,283,000	23,845,000
Bank-issued trust preferred securities
Schedule of Available-for-sale Securities
Amortized Cost	5,163,000	5,146,000
Gross Unrealized Gains	47,000	0
Gross Unrealized Losses	(427,000)	(511,000)
Available-for-sale securities	4,783,000	4,635,000
Equity securities
Schedule of Available-for-sale Securities
Amortized Cost	1,940,000	1,693,000
Gross Unrealized Gains	5,914,000	4,627,000
Gross Unrealized Losses	(69,000)	(84,000)
Available-for-sale securities	$ 7,785,000	$ 6,236,000