Loans and Allowance for Loan Losses, Allowance for Credit Losses (Details) - USD ($)		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				$ 58,349,769	$ 58,980,475
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		$ 58,980,000	$ 65,432,000
Charged-off loans		(5,161,951)	(9,226,906)
Recovery of previously charged-off loans		881,000	2,141,000
Provision for loan losses		3,651,022	3,893,570
Ending Balance		58,350,000	62,239,000
Collectively evaluated for impairment				56,454,000	57,888,000
Individually evaluated for impairment				1,896,000	1,092,000
Loans acquired with deteriorated credit quality		58,980,000	65,432,000	58,350,000	58,980,000
Collectively evaluated for impairment				8,602,391,000	8,407,340,000
Individually evaluated for impairment				32,363,000	33,750,000
Ending Balance		8,642,032,280
Troubled debt restructurings performing as of restructure date				14,600,000	15,000,000
Loans and other extensions of credit granted to directors, executive officers, and their related entities				21,800,000	22,600,000
Amount drawn from loans and other extensions of credit granted				15,000,000	14,800,000
Commercial loans held-for-sale				15,354,496
Loans sold		160,740,441	163,949,000
Mortgage loans held-for-sale				70,597,985	47,710,120
Gain on mortgage loans sold, net		4,154,952	3,567,551
Receivables Acquired with Deteriorated Credit Quality [Member]
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		0
Ending Balance		0
Loans acquired with deteriorated credit quality		0		0	0
Loans acquired with deteriorated credit quality				7,278,000	8,835,000
Commercial Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				14,168,000	13,655,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		13,655,000	15,513,000
Charged-off loans		0	0
Recovery of previously charged-off loans		6,000	58,000
Provision for loan losses		507,000	(2,020,000)
Ending Balance		14,168,000	13,551,000
Collectively evaluated for impairment				14,105,000	13,595,000
Individually evaluated for impairment				63,000	60,000
Loans acquired with deteriorated credit quality		13,655,000	15,513,000	14,168,000	13,655,000
Collectively evaluated for impairment				3,177,324,000	3,188,362,000
Individually evaluated for impairment				2,714,000	2,750,000
Ending Balance		3,181,584,000
Commercial Real Estate - Mortgage [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		0
Ending Balance		0
Loans acquired with deteriorated credit quality		0		0	0
Loans acquired with deteriorated credit quality				1,546,000	2,384,000
Consumer Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				7,219,000	6,564,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		6,564,000	7,220,000
Charged-off loans		(61,000)	(199,000)
Recovery of previously charged-off loans		170,000	85,000
Provision for loan losses		546,000	63,000
Ending Balance		7,219,000	7,169,000
Collectively evaluated for impairment				6,132,000	5,874,000
Individually evaluated for impairment				1,087,000	690,000
Loans acquired with deteriorated credit quality		6,564,000	7,220,000	7,219,000	6,564,000
Collectively evaluated for impairment				1,184,618,000	1,174,456,000
Individually evaluated for impairment				9,276,000	8,941,000
Ending Balance		1,196,375,000
Consumer Real Estate - Mortgage [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		0
Ending Balance		0
Loans acquired with deteriorated credit quality		0		0	0
Loans acquired with deteriorated credit quality				2,481,000	2,520,000
Construction and Land Development [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				4,441,000	3,624,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		3,624,000	2,903,000
Charged-off loans		0	0
Recovery of previously charged-off loans		33,000	25,000
Provision for loan losses		784,000	1,014,000
Ending Balance		4,441,000	3,942,000
Collectively evaluated for impairment				4,422,000	3,604,000
Individually evaluated for impairment				19,000	20,000
Loans acquired with deteriorated credit quality		3,624,000	2,903,000	4,441,000	3,624,000
Collectively evaluated for impairment				1,011,015,000	906,053,000
Individually evaluated for impairment				1,094,000	3,212,000
Ending Balance		1,015,127,000
Construction and Land Development [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		0
Ending Balance		0
Loans acquired with deteriorated credit quality		0		0	0
Loans acquired with deteriorated credit quality				3,018,000	3,408,000
Commercial and Industrial [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				22,912,000	24,743,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		24,743,000	23,643,000
Charged-off loans		(1,158,000)	(1,624,000)
Recovery of previously charged-off loans		140,000	1,433,000
Provision for loan losses		(813,000)	692,000
Ending Balance		22,912,000	24,144,000
Collectively evaluated for impairment				22,650,000	24,648,000
Individually evaluated for impairment				262,000	95,000
Loans acquired with deteriorated credit quality		24,743,000	23,643,000	22,912,000	24,743,000
Collectively evaluated for impairment				2,962,189,000	2,872,856,000
Individually evaluated for impairment				18,418,000	18,331,000
Ending Balance		2,980,840,000
Commercial and Industrial [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		0
Ending Balance		0
Loans acquired with deteriorated credit quality		0		0	0
Loans acquired with deteriorated credit quality				233,000	523,000
Consumer and Other [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				8,477,000	9,520,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		9,520,000	15,616,000
Charged-off loans		(3,943,000)	(7,404,000)
Recovery of previously charged-off loans		532,000	540,000
Provision for loan losses		2,368,000	3,106,000
Ending Balance		8,477,000	11,858,000
Collectively evaluated for impairment				8,012,000	9,293,000
Individually evaluated for impairment				465,000	227,000
Loans acquired with deteriorated credit quality		9,520,000	15,616,000	8,477,000	9,520,000
Collectively evaluated for impairment				267,245,000	265,613,000
Individually evaluated for impairment				861,000	516,000
Ending Balance		268,106,000
Consumer and Other [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		0
Ending Balance		0
Loans acquired with deteriorated credit quality		0		0	0
Loans acquired with deteriorated credit quality				0	0
Unallocated [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				1,133,000	874,000
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		874,000	537,000
Charged-off loans		0	0
Recovery of previously charged-off loans		0	0
Provision for loan losses		259,000	1,038,000
Ending Balance		1,133,000	1,575,000
Collectively evaluated for impairment				1,133,000	874,000
Individually evaluated for impairment				0	0
Loans acquired with deteriorated credit quality		874,000	$ 537,000	1,133,000	874,000
Unallocated [Member] | Receivables Acquired with Deteriorated Credit Quality [Member]
Changes in allowance for loan losses [Roll Forward]
Beginning Balance		0
Ending Balance		0
Loans acquired with deteriorated credit quality		0		0	0
Accruing Loans [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				55,321,000	57,014,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		8,602,391,000
Accruing Loans [Member] | Commercial Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				14,105,000	13,595,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		3,177,324,000
Accruing Loans [Member] | Consumer Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				6,132,000	5,874,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		1,184,618,000
Accruing Loans [Member] | Construction and Land Development [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				4,422,000	3,604,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		1,011,015,000
Accruing Loans [Member] | Commercial and Industrial [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				22,650,000	24,648,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		2,962,189,000
Accruing Loans [Member] | Consumer and Other [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				8,012,000	9,293,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		267,245,000
Accruing Loans [Member] | Unallocated [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				0	0
Nonaccrual Loans [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				1,852,000	1,071,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance	[1]	25,050,000
Nonaccrual Loans [Member] | Commercial Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				63,000	59,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance	[1]	4,050,000
Nonaccrual Loans [Member] | Consumer Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				1,085,000	688,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance	[1]	8,809,000
Nonaccrual Loans [Member] | Construction and Land Development [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				19,000	20,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance	[1]	4,112,000
Nonaccrual Loans [Member] | Commercial and Industrial [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				220,000	77,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance	[1]	7,257,000
Nonaccrual Loans [Member] | Consumer and Other [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				465,000	227,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance	[1]	822,000
Nonaccrual Loans [Member] | Unallocated [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses				0	0
Troubled Debt Restructurings [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	[2]			44,000	21,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		14,591,000
Troubled Debt Restructurings [Member] | Commercial Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	[2]			0	1,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		210,000
Troubled Debt Restructurings [Member] | Consumer Real Estate - Mortgage [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	[2]			2,000	2,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		2,948,000
Troubled Debt Restructurings [Member] | Construction and Land Development [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	[2]			0	0
Changes in allowance for loan losses [Roll Forward]
Ending Balance		0
Troubled Debt Restructurings [Member] | Commercial and Industrial [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	[2]			42,000	18,000
Changes in allowance for loan losses [Roll Forward]
Ending Balance		11,394,000
Troubled Debt Restructurings [Member] | Consumer and Other [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	[2]			0	0
Changes in allowance for loan losses [Roll Forward]
Ending Balance		$ 39,000
Troubled Debt Restructurings [Member] | Unallocated [Member]
Allowance allocation by loan classification for accruing and impaired loans [Abstract]
Total Allowance for Loan Losses	[2]			$ 0	$ 0

[1] Included in nonaccrual loans at March 31, 2017 and December 31, 2016 are $7.3 million and $8.8 million, respectively, in purchase credit impaired loans acquired with deteriorated credit quality.

[2] Troubled debt restructurings of $14.6 million and $15.0 million as of both March 31, 2017 and December 31, 2016, respectively, are classified as impaired loans pursuant to U.S. GAAP; however, these loans continue to accrue interest at contractual rates.