Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Loan portfolio not subject to risk rating
Total	$ 9,122,907	$ 7,620,322
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,313,344	1,039,393
Real estate – construction
Loan portfolio not subject to risk rating
Total	736,985	633,389
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,762,683	2,343,721
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	4,112,585	3,427,530
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	197,310	176,289
Purchased loans
Loan portfolio not subject to risk rating
Total	2,912,669	2,031,766
Purchased loans | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	721,742	520,075
Purchased loans | Performing
Loan portfolio not subject to risk rating
Total	719,284	518,604
Purchased loans | Non-Performing
Loan portfolio not subject to risk rating
Total	2,458	1,471
Purchased loans | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	495,545	275,570
Purchased loans | Commercial, financial, agricultural | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	11,682	11,262
Purchased loans | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total	11,613	11,216
Purchased loans | Commercial, financial, agricultural | Non-Performing
Loan portfolio not subject to risk rating
Total	69	46
Purchased loans | Real estate – construction
Loan portfolio not subject to risk rating
Total	112,093	85,731
Purchased loans | Real estate – construction | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	33,879	4,511
Purchased loans | Real estate – construction | Performing
Loan portfolio not subject to risk rating
Total	33,879	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	761,913	614,187
Purchased loans | Real estate – 1-4 family mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	565,000	460,179
Purchased loans | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total	562,989	459,038
Purchased loans | Real estate – 1-4 family mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	2,011	1,141
Purchased loans | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	1,503,075	1,037,454
Purchased loans | Real estate – commercial mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	77,838	27,618
Purchased loans | Real estate – commercial mortgage | Performing
Loan portfolio not subject to risk rating
Total	77,722	27,495
Purchased loans | Real estate – commercial mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	116	123
Purchased loans | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	40,043	18,824
Purchased loans | Installment loans to individuals | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	33,343	16,505
Purchased loans | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total	33,081	16,344
Purchased loans | Installment loans to individuals | Non-Performing
Loan portfolio not subject to risk rating
Total	$ 262	$ 161