Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Loan portfolio not subject to risk rating
Total	$ 9,313,784	$ 9,083,129
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,328,560	1,295,912
Real estate – construction
Loan portfolio not subject to risk rating
Total	816,695	740,668
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,797,633	2,795,343
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	4,022,375	4,051,509
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	348,521	199,697
Purchased loans
Loan portfolio not subject to risk rating
Total	2,281,966	2,693,417
Purchased loans | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	592,719	619,073
Purchased loans | Performing
Loan portfolio not subject to risk rating
Total	588,458	614,814
Purchased loans | Non-Performing
Loan portfolio not subject to risk rating
Total	4,261	4,259
Purchased loans | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	339,693	420,263
Purchased loans | Commercial, financial, agricultural | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	14,306	21,372
Purchased loans | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total	14,012	21,303
Purchased loans | Commercial, financial, agricultural | Non-Performing
Loan portfolio not subject to risk rating
Total	294	69
Purchased loans | Real estate – construction
Loan portfolio not subject to risk rating
Total	52,106	105,149
Purchased loans | Real estate – construction | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	2,070	3,185
Purchased loans | Real estate – construction | Performing
Loan portfolio not subject to risk rating
Total	2,070	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	561,725	707,453
Purchased loans | Real estate – 1-4 family mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	434,065	530,404
Purchased loans | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total	430,549	526,699
Purchased loans | Real estate – 1-4 family mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	3,516	3,705
Purchased loans | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	1,212,905	1,423,144
Purchased loans | Real estate – commercial mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	29,734	31,136
Purchased loans | Real estate – commercial mortgage | Performing
Loan portfolio not subject to risk rating
Total	29,629	30,951
Purchased loans | Real estate – commercial mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	105	185
Purchased loans | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	115,537	37,408
Purchased loans | Installment loans to individuals | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	112,544	32,976
Purchased loans | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total	112,198	32,676
Purchased loans | Installment loans to individuals | Non-Performing
Loan portfolio not subject to risk rating
Total	$ 346	$ 300