Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Loan portfolio not subject to risk rating
Total	$ 9,054,654	$ 9,083,129
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,305,076	1,295,912
Real estate – construction
Loan portfolio not subject to risk rating
Total	781,531	740,668
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,765,472	2,795,343
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	4,017,969	4,051,509
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	184,606	199,697
Purchased loans
Loan portfolio not subject to risk rating
Total	2,350,366	2,693,417
Purchased loans | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	530,175	619,073
Purchased loans | Performing
Loan portfolio not subject to risk rating
Total	526,138	614,814
Purchased loans | Non-Performing
Loan portfolio not subject to risk rating
Total	4,037	4,259
Purchased loans | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	374,478	420,263
Purchased loans | Commercial, financial, agricultural | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	14,055	21,372
Purchased loans | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total	14,006	21,303
Purchased loans | Commercial, financial, agricultural | Non-Performing
Loan portfolio not subject to risk rating
Total	49	69
Purchased loans | Real estate – construction
Loan portfolio not subject to risk rating
Total	65,402	105,149
Purchased loans | Real estate – construction | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	1,849	3,185
Purchased loans | Real estate – construction | Performing
Loan portfolio not subject to risk rating
Total	1,849	3,185
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	604,855	707,453
Purchased loans | Real estate – 1-4 family mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	458,995	530,404
Purchased loans | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total	455,510	526,699
Purchased loans | Real estate – 1-4 family mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	3,485	3,705
Purchased loans | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	1,276,567	1,423,144
Purchased loans | Real estate – commercial mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	29,555	31,136
Purchased loans | Real estate – commercial mortgage | Performing
Loan portfolio not subject to risk rating
Total	29,447	30,951
Purchased loans | Real estate – commercial mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	108	185
Purchased loans | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	29,064	37,408
Purchased loans | Installment loans to individuals | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	25,721	32,976
Purchased loans | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total	25,326	32,676
Purchased loans | Installment loans to individuals | Non-Performing
Loan portfolio not subject to risk rating
Total	$ 395	$ 300