Loans and the Allowance for Loan Losses - (Details 1) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Past due and nonaccrual loans
Total loans, gross	$ 5,967,302	$ 5,414,625
Unearned income	(1,873)	(1,163)
Total loans, net	5,965,429	5,413,462
Commercial, financial, agricultural
Past due and nonaccrual loans
Total loans, gross	682,936	636,837
Lease financing
Past due and nonaccrual loans
Total loans, gross	44,989	35,978
Real estate – construction
Past due and nonaccrual loans
Total loans, gross	452,731	357,665
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Total loans, gross	1,849,046	1,735,323
Real estate – commercial mortgage
Past due and nonaccrual loans
Total loans, gross	2,823,676	2,533,729
Installment loans to individuals
Past due and nonaccrual loans
Total loans, gross	113,924	115,093
Accruing Loans
Past due and nonaccrual loans
Current Loans	5,902,663	5,352,365
Unearned income	(1,873)	(1,163)
Total loans, net	5,939,465	5,384,428
Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans	678,795	634,037
Total loans, gross	681,598	636,410
Accruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans	44,989	35,978
Total loans, gross	44,989	35,978
Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans	450,574	357,420
Total loans, gross	452,731	357,665
Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans	1,823,323	1,707,230
Total loans, gross	1,837,985	1,722,883
Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans	2,793,656	2,504,192
Total loans, gross	2,810,271	2,517,622
Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans	113,199	114,671
Total loans, gross	113,764	115,033
Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	16,409	21,796
Unearned income	0	0
Total loans, net	25,964	29,034
Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans	580	264
Total loans, gross	1,338	427
Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	0	0
Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	0	0
Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans	7,663	8,249
Total loans, gross	11,061	12,440
Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans	8,043	13,276
Total loans, gross	13,405	16,107
Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans	123	7
Total loans, gross	160	60
30-89 Days Past Due | Accruing Loans
Past due and nonaccrual loans
Loans past due	19,648	15,670
30-89 Days Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	1,337	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	1,482	69
30-89 Days Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	8,736	9,196
30-89 Days Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	7,802	4,849
30-89 Days Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	291	260
30-89 Days Past Due | Nonaccruing Loans
Past due and nonaccrual loans
Loans past due	2,313	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	180	528
30-89 Days Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	2,133	568
30-89 Days Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	0	0
90 Days or More Past Due | Accruing Loans
Past due and nonaccrual loans
Loans past due	17,154	16,393
90 Days or More Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	1,466	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	675	176
90 Days or More Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	5,926	6,457
90 Days or More Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	8,813	8,581
90 Days or More Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	274	102
90 Days or More Past Due | Nonaccruing Loans
Past due and nonaccrual loans
Loans past due	7,242	6,112
90 Days or More Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	758	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	3,218	3,663
90 Days or More Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	3,229	2,263
90 Days or More Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	$ 37	$ 53