Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Loan portfolio not subject to risk rating
Total	$ 7,448,608	$ 6,202,709
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,008,935	717,490
Real estate – construction
Loan portfolio not subject to risk rating
Total	577,720	552,679
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,295,852	1,878,177
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	3,390,389	2,898,895
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	175,712	155,468
Purchased loans
Loan portfolio not subject to risk rating
Total	2,155,141	1,489,137
Purchased loans | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	545,689	316,127
Purchased loans | Performing
Loan portfolio not subject to risk rating
Total	543,727	313,852
Purchased loans | Non-Performing
Loan portfolio not subject to risk rating
Total	1,962	2,275
Purchased loans | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	301,100	128,200
Purchased loans | Commercial, financial, agricultural | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	10,799	9,568
Purchased loans | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total	10,741	9,489
Purchased loans | Commercial, financial, agricultural | Non-Performing
Loan portfolio not subject to risk rating
Total	58	79
Purchased loans | Real estate – construction
Loan portfolio not subject to risk rating
Total	100,082	68,753
Purchased loans | Real estate – construction | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	7,257	4,067
Purchased loans | Real estate – construction | Performing
Loan portfolio not subject to risk rating
Total	7,257	3,601
Purchased loans | Real estate – construction | Non-Performing
Loan portfolio not subject to risk rating
Total	0	466
Purchased loans | Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	651,792	452,447
Purchased loans | Real estate – 1-4 family mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	480,689	267,201
Purchased loans | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total	479,069	265,697
Purchased loans | Real estate – 1-4 family mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	1,620	1,504
Purchased loans | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	1,079,049	823,758
Purchased loans | Real estate – commercial mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	26,210	21,411
Purchased loans | Real estate – commercial mortgage | Performing
Loan portfolio not subject to risk rating
Total	26,088	21,353
Purchased loans | Real estate – commercial mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	122	58
Purchased loans | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	23,118	15,979
Purchased loans | Installment loans to individuals | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	20,734	13,880
Purchased loans | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total	20,572	13,712
Purchased loans | Installment loans to individuals | Non-Performing
Loan portfolio not subject to risk rating
Total	$ 162	$ 168