Non 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
Non-Purchased
Loan portfolio not subject to risk rating
Total	5,588,556	4,713,572
Non-Purchased | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	2,210,289	1,905,205
Non-Purchased | Performing
Loan portfolio not subject to risk rating
Total	2,203,941	1,900,508
Non-Purchased | Non-Performing
Loan portfolio not subject to risk rating
Total	6,348	4,697
Non-Purchased | Commercial, financial, agricultural | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	192,982	149,586
Non-Purchased | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total	191,473	148,499
Non-Purchased | Commercial, financial, agricultural | Non-Performing
Loan portfolio not subject to risk rating
Total	1,509	1,087
Non-Purchased | Lease financing | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	54,013	46,841
Non-Purchased | Lease financing | Performing
Loan portfolio not subject to risk rating
Total	53,854	46,703
Non-Purchased | Lease financing | Non-Performing
Loan portfolio not subject to risk rating
Total	159	138
Non-Purchased | Real estate – construction | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	63,417	81,377
Non-Purchased | Real estate – construction | Performing
Loan portfolio not subject to risk rating
Total	63,417	81,377
Non-Purchased | Real estate – construction | Non-Performing
Loan portfolio not subject to risk rating
Total	0	0
Non-Purchased | Real estate – 1-4 family mortgage | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	1,465,689	1,225,345
Non-Purchased | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total	1,462,347	1,222,816
Non-Purchased | Real estate – 1-4 family mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	3,342	2,529
Non-Purchased | Real estate – commercial mortgage | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	331,657	309,408
Non-Purchased | Real estate – commercial mortgage | Performing
Loan portfolio not subject to risk rating
Total	330,441	308,609
Non-Purchased | Real estate – commercial mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	1,216	799
Non-Purchased | Installment loans to individuals | Performing and Non-Performing
Loan portfolio not subject to risk rating
Total	102,531	92,648
Non-Purchased | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total	102,409	92,504
Non-Purchased | Installment loans to individuals | Non-Performing
Loan portfolio not subject to risk rating
Total	$ 122	$ 144