Loans and the Allowance for Loan Losses - (Details 1) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Past due and nonaccrual loans
Loans and Leases Receivable, Gross		$ 4,037,527	$ 3,988,187
Loans and Leases Receivable, Net of Deferred Income		4,037,204	3,987,874
Commercial, financial, agricultural
Past due and nonaccrual loans
Loans and Leases Receivable, Gross		480,559	483,283
Loans and Leases Receivable, Net of Deferred Income		480,559	483,283
Lease financing
Past due and nonaccrual loans
Loans and Leases Receivable, Gross		17,956	10,427
Real estate – construction
Past due and nonaccrual loans
Loans and Leases Receivable, Gross		212,576	212,061
Loans and Leases Receivable, Net of Deferred Income		212,576	212,061
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans and Leases Receivable, Gross		1,275,914	1,236,360
Loans and Leases Receivable, Net of Deferred Income		1,275,914	1,236,360
Real estate – commercial mortgage
Past due and nonaccrual loans
Loans and Leases Receivable, Gross		1,962,989	1,956,914
Loans and Leases Receivable, Net of Deferred Income		1,962,989	1,956,914
Installment loans to individuals
Past due and nonaccrual loans
Loans and Leases Receivable, Gross		87,533	89,142
Loans and Leases Receivable, Net of Deferred Income	[1]	105,166	99,256
Unearned income
Past due and nonaccrual loans
Loans and Leases Receivable, Gross		(323)	(313)
Accruing Loans
Past due and nonaccrual loans
Current Loans		3,978,043	3,915,598
Total Loans, Accruing		4,001,118	3,943,477
Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans		478,768	480,332
Total Loans, Accruing		479,787	482,081
Accruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans		17,541	9,965
Total Loans, Accruing		17,541	10,427
Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans		212,427	211,860
Total Loans, Accruing		212,576	211,897
Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans		1,256,170	1,212,214
Total Loans, Accruing		1,262,784	1,222,994
Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans		1,926,430	1,912,758
Total Loans, Accruing		1,941,286	1,927,319
Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans		87,030	88,782
Total Loans, Accruing		87,467	89,072
Accruing Loans | Unearned income
Past due and nonaccrual loans
Current Loans		(323)	(313)
Total Loans, Accruing		(323)	(313)
Nonaccruing Loans
Past due and nonaccrual loans
Current Loans		16,541	19,625
Total Loans, Nonaccuring		36,086	44,397
Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans		319	366
Total Loans, Nonaccuring		772	1,202
Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans		0	0
Total Loans, Nonaccuring		415	0
Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans		0	0
Total Loans, Nonaccuring		0	164
Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans		6,560	8,407
Total Loans, Nonaccuring		13,130	13,366
Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans		9,662	10,841
Total Loans, Nonaccuring		21,703	29,595
Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans		0	11
Total Loans, Nonaccuring		66	70
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		8,170	10,713
90 Days or More Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due		602	636
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		37	37
90 Days or More Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due		1,832	2,382
90 Days or More Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due		5,651	7,637
90 Days or More Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due		48	21
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		18,036	22,575
90 Days or More Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due		436	820
90 Days or More Past Due | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due		415	0
90 Days or More Past Due | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due		0	164
90 Days or More Past Due | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due		5,903	4,604
90 Days or More Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due		11,224	16,928
90 Days or More Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due		58	59
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		14,905	17,166
30-89 Days Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due		417	1,113
30-89 Days Past Due | Accruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due		0	462
30-89 Days Past Due | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due		112	0
30-89 Days Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due		4,782	8,398
30-89 Days Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due		9,205	6,924
30-89 Days Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due		389	269
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		1,509	2,197
30-89 Days Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due		17	16
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		667	355
30-89 Days Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due		817	1,826
30-89 Days Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due		8	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.