Securities (Details) - USD ($)	Mar. 31, 2017	Dec. 31, 2016
Securities available-for-sale [Abstract]
Amortized Cost	$ 1,592,531,000	$ 1,310,071,000
Gross Unrealized Gains	9,077,000	8,557,000
Gross Unrealized Losses	21,832,000	20,082,000
Fair Value	1,579,776,402	1,298,546,056
Available-for-sale, Amortized Cost [Abstract]
Due in one year or less	2,519,000
Due in one year to five years	45,041,000
Due in five years to ten years	128,637,000
Due after ten years	103,721,000
Mortgage-backed securities	1,240,671,000
Asset-backed securities	71,942,000
Amortized Cost	1,592,531,000
Available-for-sale, Fair Value [Abstract]
Due in one year or less	2,536,000
Due in one year to five years	46,143,000
Due in five years to ten years	130,524,000
Due after ten years	102,275,000
Mortgage-backed securities	1,226,977,000
Asset-backed securities	71,321,000
Available-for-sale Securities	1,579,776,402	1,298,546,056
Securities pledged as collateral to secure public funds and other deposits or securities sold under agreements to repurchase	1,045,000
Secured borrowing under agreement to repurchase	71,200,000
Securities held-to-maturity [Abstract]
Amortized Cost	24,997,568	25,251,316
Gross Unrealized Gains	124,000	87,000
Gross Unrealized Losses	86,000	105,000
Fair Value	25,035,844	25,233,254
Held-to-maturity, Amortized Cost [Abstract]
Due in one year or less	445,000
Due in one year to five years	8,262,000
Due in five years to ten years	10,817,000
Due after ten years	5,474,000
Mortgage-backed securities	0
Asset-backed securities	0
Amortized Cost	24,997,568	25,251,316
Held-to-maturity, Fair Value [Abstract]
Due in one year or less	445,000
Due in one year to five years	8,285,000
Due in five years to ten years	10,897,000
Due after ten years	5,409,000
Mortgage-backed securities	0
Asset-backed securities	0
Fair Value	25,035,844	25,233,254
Securities Pledged as Collateral [Member]
Available-for-sale, Fair Value [Abstract]
Secured borrowing under agreement to repurchase	71,200,000
US Treasury Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	250,000	250,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	250,000	250,000
Available-for-sale, Fair Value [Abstract]
Available-for-sale Securities	250,000	250,000
U.S. Government Agency Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	19,213,000	22,306,000
Gross Unrealized Gains	1,000	0
Gross Unrealized Losses	275,000	537,000
Fair Value	18,939,000	21,769,000
Available-for-sale, Fair Value [Abstract]
Available-for-sale Securities	18,939,000	21,769,000
Mortgage-backed Agency Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	1,240,671,000	988,008,000
Gross Unrealized Gains	4,205,000	4,304,000
Gross Unrealized Losses	17,899,000	15,686,000
Fair Value	1,226,977,000	976,626,000
Available-for-sale, Fair Value [Abstract]
Available-for-sale Securities	1,226,977,000	976,626,000
State and Municipal Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	247,210,000	211,581,000
Gross Unrealized Gains	4,611,000	4,103,000
Gross Unrealized Losses	2,824,000	2,964,000
Fair Value	248,997,000	212,720,000
Available-for-sale, Fair Value [Abstract]
Available-for-sale Securities	248,997,000	212,720,000
Asset-backed Securities [Member]
Securities available-for-sale [Abstract]
Amortized Cost	71,942,000	79,318,000
Gross Unrealized Gains	108,000	111,000
Gross Unrealized Losses	729,000	849,000
Fair Value	71,321,000	78,580,000
Available-for-sale, Fair Value [Abstract]
Available-for-sale Securities	71,321,000	78,580,000
Corporate Notes and Other [Member]
Securities available-for-sale [Abstract]
Amortized Cost	13,245,000	8,608,000
Gross Unrealized Gains	152,000	39,000
Gross Unrealized Losses	105,000	46,000
Fair Value	13,292,000	8,601,000
Available-for-sale, Fair Value [Abstract]
Available-for-sale Securities	13,292,000	8,601,000
State and Municipal Securities [Member]
Securities held-to-maturity [Abstract]
Gross Unrealized Gains	124,000	87,000
Gross Unrealized Losses	86,000	105,000
Fair Value	25,035,844	25,233,254
Held-to-maturity, Fair Value [Abstract]
Fair Value	$ 25,035,844	$ 25,233,254