Securities (Details) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Securities available-for-sale [Abstract]
Amortized Cost	$ 752,245,000	$ 718,685,000
Gross Unrealized Gains	20,260,000	19,530,000
Gross Unrealized Losses	3,487,000	6,161,000
Fair Value	769,018,224	732,054,785
Securities pledged as collateral to secure public funds and other deposits or securities sold under agreements to repurchase	647,200,000
Securities held-to-maturity [Abstract]
Amortized Cost	39,276,000	38,676,000
Gross Unrealized Gains	219,000	205,000
Gross Unrealized Losses	87,000	92,000
Fair Value	39,407,835	38,788,870
Available-for-sale, Amortized Cost [Abstract]
Due in one year or less	7,508,000
Due in one year to five years	31,685,000
Due in five years to ten years	151,166,000
Due after ten years	90,645,000
Mortgage-backed securities	458,901,000
Asset-backed securities	12,340,000
Amortized Cost	752,245,000
Available-for-sale, Fair Value [Abstract]
Due in one year or less	7,545,000
Due in one year to five years	33,245,000
Due in five years to ten years	156,389,000
Due after ten years	91,138,000
Mortgage-backed securities	468,362,000
Asset-backed securities	12,339,000
Fair Value	769,018,224
Held-to-maturity, Amortized Cost [Abstract]
Due in one year or less	1,694,000
Due in one year to five years	11,650,000
Due in five years to ten years	15,879,000
Due after ten years	10,053,000
Mortgage-backed securities	0
Asset-backed securities	0
Amortized Cost	39,275,846	38,675,527
Held-to-maturity, Fair Value [Abstract]
Due in one year or less	1,697,000
Due in one year to five years	11,691,000
Due in five years to ten years	15,935,000
Due after ten years	10,085,000
Mortgage-backed securities	0
Asset-backed securities	0
Fair Value	39,407,835	38,788,870
State and Municipal Securities [Member]
Securities held-to-maturity [Abstract]
Amortized Cost	39,276,000	38,676,000
Gross Unrealized Gains	219,000	205,000
Gross Unrealized Losses	87,000	92,000
Fair Value	39,407,835	38,788,870
Held-to-maturity, Fair Value [Abstract]
Fair Value	39,407,835	38,788,870
US Treasury Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	0	0
U.S. Government Agency Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	120,106,000	117,098,000
Gross Unrealized Gains	30,000	12,000
Gross Unrealized Losses	1,577,000	3,654,000
Fair Value	118,559,000	113,456,000
Mortgage-backed Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	458,901,000	447,757,000
Gross Unrealized Gains	11,147,000	10,322,000
Gross Unrealized Losses	1,686,000	2,240,000
Fair Value	468,362,000	455,839,000
State and Municipal Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	126,041,000	130,545,000
Gross Unrealized Gains	8,046,000	8,213,000
Gross Unrealized Losses	152,000	180,000
Fair Value	133,935,000	138,578,000
Asset-backed Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	12,340,000	13,089,000
Gross Unrealized Gains	15,000	14,000
Gross Unrealized Losses	16,000	85,000
Fair Value	12,339,000	13,018,000
Corporate Notes and Other [Member]
Securities available-for-sale [Abstract]
Amortized Cost	34,857,000	10,196,000
Gross Unrealized Gains	1,022,000	969,000
Gross Unrealized Losses	56,000	2,000
Fair Value	$ 35,823,000	$ 11,163,000