Non Purchased Loans - Summary of Non-Purchased Loans and Leases (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Summary of loans
Gross loans	$ 10,021,105	$ 10,937,807
Unearned income	(4,281)	(4,160)
Loans, net of unearned income	10,016,824	10,933,647	$ 11,084,738
Commercial, financial, agricultural
Summary of loans
Gross loans	1,436,019	2,536,984
Loans, net of unearned income	1,436,019		2,648,062
Lease financing
Summary of loans
Gross loans	83,496	80,022
Loans, net of unearned income	79,215		82,928
Real estate – construction:
Summary of loans
Gross loans	1,091,296	858,104
Loans, net of unearned income	1,091,296		773,119
Real estate – construction: | Residential
Summary of loans
Gross loans	307,825	246,673
Real estate – construction: | Commercial
Summary of loans
Gross loans	783,471	611,431
Real estate – 1-4 family mortgage:
Summary of loans
Gross loans	2,724,743	2,698,308
Loans, net of unearned income	2,724,743		2,760,394
Real estate – 1-4 family mortgage: | Primary
Summary of loans
Gross loans	1,808,139	1,750,951
Real estate – 1-4 family mortgage: | Home equity
Summary of loans
Gross loans	481,552	513,160
Real estate – 1-4 family mortgage: | Rental/investment
Summary of loans
Gross loans	291,116	296,364
Real estate – commercial mortgage:
Summary of loans
Gross loans	4,535,730	4,554,852
Loans, net of unearned income	4,535,730		4,577,009
Real estate – commercial mortgage: | Owner-occupied
Summary of loans
Gross loans	1,630,227	1,657,806
Real estate – commercial mortgage: | Non-owner occupied
Summary of loans
Gross loans	2,779,237	2,747,467
Installment loans to individuals
Summary of loans
Gross loans	149,821	209,537
Loans, net of unearned income	149,821		$ 243,226
Non purchased loans and leases
Summary of loans
Gross loans	8,880,161	9,423,700
Unearned income	(4,281)	(4,160)
Loans, net of unearned income	8,875,880	9,419,540
Non purchased loans and leases | Paycheck Protection Program
Summary of loans
Loans, net of unearned income	67,462	1,128,703
Non purchased loans and leases | Commercial, financial, agricultural
Summary of loans
Gross loans	1,321,569	2,360,471
Non purchased loans and leases | Lease financing
Summary of loans
Gross loans	83,496	80,022
Non purchased loans and leases | Real estate – construction:
Summary of loans
Gross loans	1,086,303	827,152
Non purchased loans and leases | Real estate – construction: | Residential
Summary of loans
Gross loans	306,537	243,814
Non purchased loans and leases | Real estate – construction: | Commercial
Summary of loans
Gross loans	779,766	583,338
Non purchased loans and leases | Real estate – 1-4 family mortgage:
Summary of loans
Gross loans	2,484,396	2,356,564
Non purchased loans and leases | Real estate – 1-4 family mortgage: | Primary
Summary of loans
Gross loans	1,657,195	1,536,181
Non purchased loans and leases | Real estate – 1-4 family mortgage: | Home equity
Summary of loans
Gross loans	424,860	432,768
Non purchased loans and leases | Real estate – 1-4 family mortgage: | Rental/investment
Summary of loans
Gross loans	268,609	264,436
Non purchased loans and leases | Real estate – 1-4 family mortgage: | Land development
Summary of loans
Gross loans	133,732	123,179
Non purchased loans and leases | Real estate – commercial mortgage:
Summary of loans
Gross loans	3,794,898	3,649,629
Non purchased loans and leases | Real estate – commercial mortgage: | Land development
Summary of loans
Gross loans	106,475	120,125
Non purchased loans and leases | Real estate – commercial mortgage: | Owner-occupied
Summary of loans
Gross loans	1,365,288	1,334,765
Non purchased loans and leases | Real estate – commercial mortgage: | Non-owner occupied
Summary of loans
Gross loans	2,323,135	2,194,739
Non purchased loans and leases | Installment loans to individuals
Summary of loans
Gross loans	$ 109,499	$ 149,862