Loans and the Allowance for Loan Losses (Details 1) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Past due and nonaccrual loans
Loans and Leases Receivable, Gross	$ 3,957,626		$ 3,881,019
Loans and Leases Receivable, Net of Deferred Income	3,957,439		3,881,018
Commercial, financial, agricultural
Past due and nonaccrual loans
Loans and Leases Receivable, Gross	450,559		468,963
Loans and Leases Receivable, Net of Deferred Income	450,559		468,963
Lease financing
Past due and nonaccrual loans
Loans and Leases Receivable, Gross	5,564		53
Real estate – construction
Past due and nonaccrual loans
Loans and Leases Receivable, Gross	197,066		161,436
Loans and Leases Receivable, Net of Deferred Income	197,066		161,436
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans and Leases Receivable, Gross	1,221,579		1,208,233
Loans and Leases Receivable, Net of Deferred Income	1,221,579		1,208,233
Real estate – commercial mortgage
Past due and nonaccrual loans
Loans and Leases Receivable, Gross	1,991,052		1,950,572
Loans and Leases Receivable, Net of Deferred Income	1,991,052		1,950,572
Installment loans to individuals
Past due and nonaccrual loans
Loans and Leases Receivable, Gross	91,806		91,762
Loans and Leases Receivable, Net of Deferred Income	97,183	[1]	91,814	[1]
Unearned income
Past due and nonaccrual loans
Loans and Leases Receivable, Gross	(187)		(1)
Accruing Loans
Past due and nonaccrual loans
30-89 Days Past Due	16,248		22,475
90 Days or More Past Due	17,531		4,187
Current Loans	3,869,383		3,782,025
Total Loans, Accruing	3,903,162		3,808,687
Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
30-89 Days Past Due	1,056		2,067
90 Days or More Past Due	599		607
Current Loans	446,907		463,521
Total Loans, Accruing	448,562		466,195
Accruing Loans | Lease financing
Past due and nonaccrual loans
30-89 Days Past Due	0		0
90 Days or More Past Due	0		0
Current Loans	5,564		53
Total Loans, Accruing	5,564		53
Accruing Loans | Real estate – construction
Past due and nonaccrual loans
30-89 Days Past Due	237		664
90 Days or More Past Due	281		0
Current Loans	194,900		159,124
Total Loans, Accruing	195,418		159,788
Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
30-89 Days Past Due	6,739		10,168
90 Days or More Past Due	5,248		2,206
Current Loans	1,193,594		1,179,703
Total Loans, Accruing	1,205,581		1,192,077
Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
30-89 Days Past Due	7,966		8,870
90 Days or More Past Due	11,381		1,286
Current Loans	1,937,174		1,888,745
Total Loans, Accruing	1,956,521		1,898,901
Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
30-89 Days Past Due	250		706
90 Days or More Past Due	22		88
Current Loans	91,431		90,880
Total Loans, Accruing	91,703		91,674
Accruing Loans | Unearned income
Past due and nonaccrual loans
30-89 Days Past Due	0		0
90 Days or More Past Due	0		0
Current Loans	(187)		(1)
Total Loans, Accruing	(187)		(1)
Nonaccruing Loans
Past due and nonaccrual loans
30-89 Days Past Due	3,499		2,307
90 Days or More Past Due	29,691		47,167
Current Loans	21,087		22,857
Total Loans, Nonaccuring	54,277		72,331
Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
30-89 Days Past Due	650		138
90 Days or More Past Due	953		1,959
Current Loans	394		671
Total Loans, Nonaccuring	1,997		2,768
Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
30-89 Days Past Due	0		0
90 Days or More Past Due	0		0
Current Loans	0		0
Total Loans, Nonaccuring	0		0
Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
30-89 Days Past Due	0		0
90 Days or More Past Due	1,648		1,648
Current Loans	0		0
Total Loans, Nonaccuring	1,648		1,648
Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
30-89 Days Past Due	208		1,203
90 Days or More Past Due	6,197		6,041
Current Loans	9,593		8,912
Total Loans, Nonaccuring	15,998		16,156
Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
30-89 Days Past Due	2,641		966
90 Days or More Past Due	20,803		37,439
Current Loans	11,087		13,266
Total Loans, Nonaccuring	34,531		51,671
Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
30-89 Days Past Due	0		0
90 Days or More Past Due	90		80
Current Loans	13		8
Total Loans, Nonaccuring	103		88
Nonaccruing Loans | Unearned income
Past due and nonaccrual loans
30-89 Days Past Due	0		0
90 Days or More Past Due	0		0
Current Loans	0		0
Total Loans, Nonaccuring	$ 0		$ 0

[1] Includes lease financing receivables.