Investment Securities Available-for-sale Securities (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities
Amortized Cost	$ 777,017,000	$ 780,304,000
Gross Unrealized Gains	12,695,000	13,196,000
Gross Unrealized Losses	(11,772,000)	(8,799,000)
Fair Value	777,940,000	784,701,000
Securities of a single issuer, other than US Treasury, government agencies and US government sponsored agencies exceeding 10% of Stockholders' Equity	0
U.S. government sponsored agencies
Schedule of Available-for-sale Securities
Amortized Cost	1,000,000	2,908,000
Gross Unrealized Gains	0	58,000
Gross Unrealized Losses	0	0
Fair Value	1,000,000	2,966,000
States and political subdivisions
Schedule of Available-for-sale Securities
Amortized Cost	115,657,000	111,283,000
Gross Unrealized Gains	1,836,000	3,487,000
Gross Unrealized Losses	(263,000)	(44,000)
Fair Value	117,230,000	114,726,000
Residential mortgage-backed securities
Schedule of Available-for-sale Securities
Amortized Cost	633,802,000	635,504,000
Gross Unrealized Gains	3,758,000	4,905,000
Gross Unrealized Losses	(10,993,000)	(8,116,000)
Fair Value	626,567,000	632,293,000
Commercial mortgage-backed securities
Schedule of Available-for-sale Securities
Amortized Cost	19,337,000	23,770,000
Gross Unrealized Gains	41,000	119,000
Gross Unrealized Losses	(87,000)	(44,000)
Fair Value	19,291,000	23,845,000
Bank-issued trust preferred securities
Schedule of Available-for-sale Securities
Amortized Cost	5,169,000	5,146,000
Gross Unrealized Gains	91,000	0
Gross Unrealized Losses	(361,000)	(511,000)
Fair Value	4,899,000	4,635,000
Equity securities
Schedule of Available-for-sale Securities
Amortized Cost	2,052,000	1,693,000
Gross Unrealized Gains	6,969,000	4,627,000
Gross Unrealized Losses	(68,000)	(84,000)
Fair Value	$ 8,953,000	$ 6,236,000