Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Loan portfolio not subject to risk rating
Total	$ 7,767,657	$ 7,620,322
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	987,818	1,039,393
Real estate – construction
Loan portfolio not subject to risk rating
Total	712,818	633,389
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,433,099	2,343,721
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	3,461,174	3,427,530
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	172,748	176,289
Purchased loans
Loan portfolio not subject to risk rating
Total	1,709,891	2,031,766
Purchased loans | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	447,237	520,075
Purchased loans | Performing
Loan portfolio not subject to risk rating
Total	445,102	518,604
Purchased loans | Non-Performing
Loan portfolio not subject to risk rating
Total	2,135	1,471
Purchased loans | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	197,455	275,570
Purchased loans | Commercial, financial, agricultural | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	10,463	11,262
Purchased loans | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total	10,424	11,216
Purchased loans | Commercial, financial, agricultural | Non-Performing
Loan portfolio not subject to risk rating
Total	39	46
Purchased loans | Real estate – construction
Loan portfolio not subject to risk rating
Total	70,438	85,731
Purchased loans | Real estate – construction | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	1,028	4,511
Purchased loans | Real estate – construction | Performing
Loan portfolio not subject to risk rating
Total	1,028	4,511
Purchased loans | Real estate – construction | Non-Performing
Loan portfolio not subject to risk rating
Total	0	0
Purchased loans | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	520,649	614,187
Purchased loans | Real estate – 1-4 family mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	392,450	460,179
Purchased loans | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total	390,746	459,038
Purchased loans | Real estate – 1-4 family mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	1,704	1,141
Purchased loans | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	906,219	1,037,454
Purchased loans | Real estate – commercial mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	30,352	27,618
Purchased loans | Real estate – commercial mortgage | Performing
Loan portfolio not subject to risk rating
Total	30,234	27,495
Purchased loans | Real estate – commercial mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	118	123
Purchased loans | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	15,130	18,824
Purchased loans | Installment loans to individuals | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	12,944	16,505
Purchased loans | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total	12,670	16,344
Purchased loans | Installment loans to individuals | Non-Performing
Loan portfolio not subject to risk rating
Total	$ 274	$ 161