Non Purchased Loans - Aging of Past Due and Nonaccrual Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Past due and nonaccrual loans
Total loans, gross	$ 9,091,181	$ 9,086,256
Unearned income	(2,888)	(3,127)
Loans, net of unearned income	9,088,293	9,083,129
Commercial, financial, agricultural
Past due and nonaccrual loans
Total loans, gross	1,308,457	1,295,912
Loans, net of unearned income	1,308,457	1,295,912
Lease financing
Past due and nonaccrual loans
Total loans, gross	61,539	64,992
Real estate – construction
Past due and nonaccrual loans
Total loans, gross	741,073	740,668
Loans, net of unearned income	741,073	740,668
Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Total loans, gross	2,769,173	2,795,343
Loans, net of unearned income	2,769,173	2,795,343
Real estate – commercial mortgage
Past due and nonaccrual loans
Total loans, gross	4,083,632	4,051,509
Loans, net of unearned income	4,083,632	4,051,509
Installment loans to individuals
Past due and nonaccrual loans
Total loans, gross	127,307	137,832
Loans, net of unearned income	185,958	199,697
Non purchased loans and leases
Past due and nonaccrual loans
Total loans, gross	6,568,487	6,392,839
Unearned income	(2,888)	(3,127)
Loans, net of unearned income	6,565,599	6,389,712
Non purchased loans and leases | Commercial, financial, agricultural
Past due and nonaccrual loans
Total loans, gross	921,081	875,649
Non purchased loans and leases | Lease financing
Past due and nonaccrual loans
Total loans, gross	61,539	64,992
Non purchased loans and leases | Real estate – construction
Past due and nonaccrual loans
Total loans, gross	651,119	635,519
Non purchased loans and leases | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Total loans, gross	2,114,908	2,087,890
Non purchased loans and leases | Real estate – commercial mortgage
Past due and nonaccrual loans
Total loans, gross	2,726,186	2,628,365
Non purchased loans and leases | Installment loans to individuals
Past due and nonaccrual loans
Total loans, gross	93,654	100,424
Non purchased loans and leases | Accruing Loans
Past due and nonaccrual loans
Current Loans	6,528,805	6,359,292
Unearned income	(2,888)	(3,127)
Loans, net of unearned income	6,553,092	6,379,494
Non purchased loans and leases | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans	913,608	870,457
Total loans, gross	916,803	874,121
Non purchased loans and leases | Accruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans	61,009	64,296
Total loans, gross	61,449	64,992
Non purchased loans and leases | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans	650,700	634,632
Total loans, gross	651,119	635,519
Non purchased loans and leases | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans	2,093,721	2,071,401
Total loans, gross	2,111,098	2,083,930
Non purchased loans and leases | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans	2,719,516	2,621,902
Total loans, gross	2,721,923	2,623,795
Non purchased loans and leases | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans	93,139	99,731
Total loans, gross	93,588	100,264
Non purchased loans and leases | Nonaccruing Loans
Past due and nonaccrual loans
Current Loans	3,382	2,814
Unearned income	0	0
Loans, net of unearned income	12,507	10,218
Non purchased loans and leases | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Current Loans	180	172
Total loans, gross	4,278	1,528
Non purchased loans and leases | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	90	0
Non purchased loans and leases | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	0	0
Non purchased loans and leases | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Current Loans	1,288	1,046
Total loans, gross	3,810	3,960
Non purchased loans and leases | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Current Loans	1,914	1,596
Total loans, gross	4,263	4,570
Non purchased loans and leases | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Current Loans	0	0
Total loans, gross	66	160
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans
Past due and nonaccrual loans
Loans past due	23,095	17,517
Unearned income	0	0
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	3,117	3,397
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due	440	607
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due	419	887
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	16,333	10,378
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	2,394	1,880
Non purchased loans and leases | 30-89 Days Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	392	368
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans
Past due and nonaccrual loans
Loans past due	2,011	241
Unearned income	0	0
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	953	0
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	1,056	238
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 30-89 Days Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	2	3
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans
Past due and nonaccrual loans
Loans past due	1,192	2,685
Unearned income	0	0
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	78	267
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due	0	89
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	1,044	2,151
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	13	13
Non purchased loans and leases | 90 Days or More Past Due | Accruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	57	165
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans
Past due and nonaccrual loans
Loans past due	7,114	7,163
Unearned income	0	0
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Commercial, financial, agricultural
Past due and nonaccrual loans
Loans past due	3,145	1,356
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Lease financing
Past due and nonaccrual loans
Loans past due	90	0
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Real estate – construction
Past due and nonaccrual loans
Loans past due	0	0
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Real estate – 1-4 family mortgage
Past due and nonaccrual loans
Loans past due	1,466	2,676
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Real estate – commercial mortgage
Past due and nonaccrual loans
Loans past due	2,349	2,974
Non purchased loans and leases | 90 Days or More Past Due | Nonaccruing Loans | Installment loans to individuals
Past due and nonaccrual loans
Loans past due	$ 64	$ 157