Loans and the Allowance for Loan Losses - (Details 1) - USD ($) $ in Thousands		Mar. 31, 2016	Dec. 31, 2015
Past due and nonaccrual loans
Loans and leases receivable, gross		$ 5,574,398	$ 5,414,625
Loans and leases receivable, net of unearned income		5,572,730	5,413,462
Commercial, financial, agricultural
Past due and nonaccrual loans
Loans and leases receivable, gross		654,934	636,837
Loans and leases receivable, net of unearned income		654,934	636,837
Lease financing
Past due and nonaccrual loans
Loans and leases receivable, gross		43,605	35,978
Real estate – construction
Past due and nonaccrual loans
Loans and leases receivable, gross		377,574	357,665
Loans and leases receivable, net of unearned income		377,574	357,665
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans and leases receivable, gross		1,777,495	1,735,323
Loans and leases receivable, net of unearned income		1,777,495	1,735,323
Real estate – commercial mortgage
Past due and nonaccrual loans
Loans and leases receivable, gross		2,607,510	2,533,729
Loans and leases receivable, net of unearned income		2,607,510	2,533,729
Installment loans to individuals
Past due and nonaccrual loans
Loans and leases receivable, gross		113,280	115,093
Loans and leases receivable, net of unearned income	[1]	155,217	149,908
Unearned income
Past due and nonaccrual loans
Loans and leases receivable, gross		(1,668)	(1,163)
Accruing Loans
Past due and nonaccrual loans
Current Loans		5,509,973	5,352,365
Total loans, accruing		5,545,964	5,384,428
Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans		651,749	634,037
Total loans, accruing		654,450	636,410
Accruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans		43,605	35,978
Total loans, accruing		43,605	35,978
Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans		376,434	357,420
Total loans, accruing		377,574	357,665
Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans		1,751,451	1,707,230
Total loans, accruing		1,767,019	1,722,883
Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans		2,575,720	2,504,192
Total loans, accruing		2,591,739	2,517,622
Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans		112,682	114,671
Total loans, accruing		113,245	115,033
Accruing Loans | Unearned income
Past due and nonaccrual loans
Current Loans		(1,668)	(1,163)
Total loans, accruing		(1,668)	(1,163)
Nonaccruing Loans
Past due and nonaccrual loans
Current Loans		22,664	21,796
Total loans, nonaccuring		26,766	29,034
Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans		248	264
Total loans, nonaccuring		484	427
Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans		0	0
Total loans, nonaccuring		0	0
Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans		0	0
Total loans, nonaccuring		0	0
Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans		7,966	8,249
Total loans, nonaccuring		10,476	12,440
Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans		14,443	13,276
Total loans, nonaccuring		15,771	16,107
Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans		7	7
Total loans, nonaccuring		35	60
Nonaccruing Loans | Unearned income
Past due and nonaccrual loans
Current Loans		0	0
Total loans, nonaccuring		0	0
90 Days or More Past Due | Accruing Loans
Past due and nonaccrual loans
Loans past due		17,643	16,393
90 Days or More Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due		1,404	1,077
90 Days or More Past Due | Accruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due		0	0
90 Days or More Past Due | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due		242	176
90 Days or More Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due		6,783	6,457
90 Days or More Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due		9,057	8,581
90 Days or More Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due		157	102
90 Days or More Past Due | Accruing Loans | Unearned income
Past due and nonaccrual loans
Loans past due		0	0
90 Days or More Past Due | Nonaccruing Loans
Past due and nonaccrual loans
Loans past due		3,838	6,112
90 Days or More Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due		236	133
90 Days or More Past Due | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due		0	0
90 Days or More Past Due | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due		0	0
90 Days or More Past Due | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due		2,256	3,663
90 Days or More Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due		1,318	2,263
90 Days or More Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due		28	53
90 Days or More Past Due | Nonaccruing Loans | Unearned income
Past due and nonaccrual loans
Loans past due		0	0
30-89 Days Past Due | Accruing Loans
Past due and nonaccrual loans
Loans past due		18,348	15,670
30-89 Days Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due		1,297	1,296
30-89 Days Past Due | Accruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due		0	0
30-89 Days Past Due | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due		898	69
30-89 Days Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due		8,785	9,196
30-89 Days Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due		6,962	4,849
30-89 Days Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due		406	260
30-89 Days Past Due | Accruing Loans | Unearned income
Past due and nonaccrual loans
Loans past due		0	0
30-89 Days Past Due | Nonaccruing Loans
Past due and nonaccrual loans
Loans past due		264	1,126
30-89 Days Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due		0	30
30-89 Days Past Due | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due		0	0
30-89 Days Past Due | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due		0	0
30-89 Days Past Due | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due		254	528
30-89 Days Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due		10	568
30-89 Days Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due		0	0
30-89 Days Past Due | Nonaccruing Loans | Unearned income
Past due and nonaccrual loans
Loans past due		$ 0	$ 0

[1] Includes lease financing receivables.