Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Loan portfolio not subject to risk rating
Total	$ 9,088,293	$ 9,083,129
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	1,308,457	1,295,912
Real estate – construction
Loan portfolio not subject to risk rating
Total	741,073	740,668
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total	2,769,173	2,795,343
Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	4,083,632	4,051,509
Installment loans to individuals
Loan portfolio not subject to risk rating
Total	185,958	199,697
Purchased loans
Loan portfolio not subject to risk rating
Total	2,522,694	2,693,417
Purchased loans | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	583,905	619,073
Purchased loans | Performing
Loan portfolio not subject to risk rating
Total	579,815	614,814
Purchased loans | Non-Performing
Loan portfolio not subject to risk rating
Total	4,090	4,259
Purchased loans | Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total	387,376	420,263
Purchased loans | Commercial, financial, agricultural | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	19,498	21,372
Purchased loans | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total	19,454	21,303
Purchased loans | Commercial, financial, agricultural | Non-Performing
Loan portfolio not subject to risk rating
Total	44	69
Purchased loans | Real estate – construction
Loan portfolio not subject to risk rating
Total	89,954	105,149
Purchased loans | Real estate – construction | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	4,284	3,185
Purchased loans | Real estate – construction | Performing
Loan portfolio not subject to risk rating
Total	4,284	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	654,265	707,453
Purchased loans | Real estate – 1-4 family mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	498,230	530,404
Purchased loans | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total	494,730	526,699
Purchased loans | Real estate – 1-4 family mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	3,500	3,705
Purchased loans | Real estate – commercial mortgage
Loan portfolio not subject to risk rating
Total	1,357,446	1,423,144
Purchased loans | Real estate – commercial mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	32,134	31,136
Purchased loans | Real estate – commercial mortgage | Performing
Loan portfolio not subject to risk rating
Total	32,023	30,951
Purchased loans | Real estate – commercial mortgage | Non-Performing
Loan portfolio not subject to risk rating
Total	111	185
Purchased loans | Installment loans to individuals
Loan portfolio not subject to risk rating
Total	33,653	37,408
Purchased loans | Installment loans to individuals | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total	29,759	32,976
Purchased loans | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total	29,324	32,676
Purchased loans | Installment loans to individuals | Non-Performing
Loan portfolio not subject to risk rating
Total	$ 435	$ 300