Purchased Loans - Performing Status (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Loan portfolio not subject to risk rating
Total	$ 7,620,322	$ 6,202,709
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,039,393	717,490
Real estate – construction
Loan portfolio not subject to risk rating
Total	633,389	552,679
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,343,721	1,878,177
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	3,427,530	2,898,895
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	176,289	155,468
Purchased
Loan portfolio not subject to risk rating
Total	2,031,766	1,489,137
Purchased | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	520,075	316,127
Purchased | Performing
Loan portfolio not subject to risk rating
Total	518,604	313,852
Purchased | Non-Performing
Loan portfolio not subject to risk rating
Total	1,471	2,275
Purchased | Commercial, financial, agricultural | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	11,262	9,568
Purchased | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total	11,216	9,489
Purchased | Commercial, financial, agricultural | Non-Performing
Loan portfolio not subject to risk rating
Total	46	79
Purchased | Lease financing | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	0	0
Purchased | Lease financing | Performing
Loan portfolio not subject to risk rating
Total	0	0
Purchased | Lease financing | Non-Performing
Loan portfolio not subject to risk rating
Total	0	0
Purchased | Real estate – construction | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	4,511	4,067
Purchased | Real estate – construction | Performing
Loan portfolio not subject to risk rating
Total	4,511	3,601
Purchased | Real estate – construction | Non-Performing
Loan portfolio not subject to risk rating
Total	0	466
Purchased | Real estate – 1-4 family mortgage | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	460,179	267,201
Purchased | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total	459,038	265,697
Purchased | Real estate – 1-4 family mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	1,141	1,504
Purchased | Real estate – commercial mortgage | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	27,618	21,411
Purchased | Real estate – commercial mortgage | Performing
Loan portfolio not subject to risk rating
Total	27,495	21,353
Purchased | Real estate – commercial mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	123	58
Purchased | Installment loans to individuals | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	16,505	13,880
Purchased | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total	16,344	13,712
Purchased | Installment loans to individuals | Non-Performing
Loan portfolio not subject to risk rating
Total	$ 161	$ 168