Non Purchased Loans - Loan Portfolio Not Subject to Risk Rating (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Loan portfolio not subject to risk rating
Loans, net of unearned income	$ 10,016,824	$ 10,933,647	$ 11,084,738
Commercial, financial, agricultural
Loan portfolio not subject to risk rating
Loans, net of unearned income	1,436,019		2,648,062
Lease financing
Loan portfolio not subject to risk rating
Loans, net of unearned income	79,215		82,928
Real estate – construction:
Loan portfolio not subject to risk rating
Loans, net of unearned income	1,091,296		773,119
Real estate – 1-4 family mortgage:
Loan portfolio not subject to risk rating
Loans, net of unearned income	2,724,743		2,760,394
Real estate – commercial mortgage:
Loan portfolio not subject to risk rating
Loans, net of unearned income	4,535,730		4,577,009
Installment loans to individuals
Loan portfolio not subject to risk rating
Loans, net of unearned income	149,821		$ 243,226
Non purchased loans and leases
Loan portfolio not subject to risk rating
Loans, net of unearned income	$ 8,875,880	$ 9,419,540