Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Loan portfolio not subject to risk rating
Total loans, net of unearned income	$ 9,769,377	$ 9,689,638
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Total loans, net of unearned income		1,367,972
Real estate – construction:
Loan portfolio not subject to risk rating
Total loans, net of unearned income		826,483
Real estate – 1-4 family mortgage
Loan portfolio not subject to risk rating
Total loans, net of unearned income		2,866,613
Real estate – commercial mortgage:
Loan portfolio not subject to risk rating
Total loans, net of unearned income		4,244,265
Installment loans to individuals
Loan portfolio not subject to risk rating
Total loans, net of unearned income		384,305
Purchased loans
Loan portfolio not subject to risk rating
Total loans, net of unearned income	$ 1,966,973	2,101,664
Purchased loans | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total loans, net of unearned income		543,747
Purchased loans | Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		539,747
Purchased loans | Non- Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		4,000
Purchased loans | Commercial, financial, agricultural | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total loans, net of unearned income		13,935
Purchased loans | Commercial, financial, agricultural | Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		13,935
Purchased loans | Commercial, financial, agricultural | Non- Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		0
Purchased loans | Real estate – construction: | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total loans, net of unearned income		1,725
Purchased loans | Real estate – construction: | Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		1,725
Purchased loans | Real estate – construction: | Non- Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		0
Purchased loans | Real estate – 1-4 family mortgage | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total loans, net of unearned income		398,114
Purchased loans | Real estate – 1-4 family mortgage | Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		394,476
Purchased loans | Real estate – 1-4 family mortgage | Non- Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		3,638
Purchased loans | Real estate – commercial mortgage: | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total loans, net of unearned income		30,573
Purchased loans | Real estate – commercial mortgage: | Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		30,472
Purchased loans | Real estate – commercial mortgage: | Non- Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		101
Purchased loans | Installment loans to individuals | Performing and Nonperforming
Loan portfolio not subject to risk rating
Total loans, net of unearned income		99,400
Purchased loans | Installment loans to individuals | Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		99,139
Purchased loans | Installment loans to individuals | Non- Performing
Loan portfolio not subject to risk rating
Total loans, net of unearned income		$ 261