Non Purchased Loans - Summary of Non-Purchased Loans and Leases (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Summary of loans
Gross loans	$ 10,692,423	$ 10,937,807
Unearned income	(4,015)	(4,160)
Loans, net of unearned income	10,688,408	10,933,647	$ 9,769,377
Commercial, financial, agricultural
Summary of loans
Gross loans	2,249,287	2,536,984
Loans, net of unearned income	2,249,287		1,424,576
Lease financing
Summary of loans
Gross loans	79,271	80,022
Loans, net of unearned income	75,256		84,679
Real estate – construction:
Summary of loans
Gross loans	955,918	858,104
Loans, net of unearned income	955,918		787,895
Real estate – construction: | Residential
Summary of loans
Gross loans	255,356	246,673
Real estate – construction: | Commercial
Summary of loans
Gross loans	700,562	611,431
Real estate – 1-4 family mortgage:
Summary of loans
Gross loans	2,686,061	2,698,308
Loans, net of unearned income	2,686,061		2,846,301
Real estate – 1-4 family mortgage: | Primary
Summary of loans
Gross loans	1,766,751	1,750,951
Real estate – 1-4 family mortgage: | Home equity
Summary of loans
Gross loans	504,620	513,160
Real estate – 1-4 family mortgage: | Rental/investment
Summary of loans
Gross loans	285,779	296,364
Real estate – commercial mortgage:
Summary of loans
Gross loans	4,549,027	4,554,852
Loans, net of unearned income	4,549,027		4,308,708
Real estate – commercial mortgage: | Owner-occupied
Summary of loans
Gross loans	1,644,770	1,657,806
Real estate – commercial mortgage: | Non-owner occupied
Summary of loans
Gross loans	2,767,869	2,747,467
Installment loans to individuals
Summary of loans
Gross loans	172,859	209,537
Loans, net of unearned income	172,859		$ 317,218
Non purchased loans and leases
Summary of loans
Gross loans	9,296,517	9,423,700
Unearned income	(4,015)	(4,160)
Loans, net of unearned income	9,292,502	9,419,540
Non purchased loans and leases | Paycheck Protection Program
Summary of loans
Loans, net of unearned income	860,864	1,128,703
Non purchased loans and leases | Commercial, financial, agricultural
Summary of loans
Gross loans	2,105,444	2,360,471
Non purchased loans and leases | Lease financing
Summary of loans
Gross loans	79,271	80,022
Non purchased loans and leases | Real estate – construction:
Summary of loans
Gross loans	933,586	827,152
Non purchased loans and leases | Real estate – construction: | Residential
Summary of loans
Gross loans	252,795	243,814
Non purchased loans and leases | Real estate – construction: | Commercial
Summary of loans
Gross loans	680,791	583,338
Non purchased loans and leases | Real estate – 1-4 family mortgage:
Summary of loans
Gross loans	2,380,920	2,356,564
Non purchased loans and leases | Real estate – 1-4 family mortgage: | Primary
Summary of loans
Gross loans	1,576,212	1,536,181
Non purchased loans and leases | Real estate – 1-4 family mortgage: | Home equity
Summary of loans
Gross loans	432,207	432,768
Non purchased loans and leases | Real estate – 1-4 family mortgage: | Rental/investment
Summary of loans
Gross loans	256,979	264,436
Non purchased loans and leases | Real estate – 1-4 family mortgage: | Land development
Summary of loans
Gross loans	115,522	123,179
Non purchased loans and leases | Real estate – commercial mortgage:
Summary of loans
Gross loans	3,676,160	3,649,629
Non purchased loans and leases | Real estate – commercial mortgage: | Land development
Summary of loans
Gross loans	110,800	120,125
Non purchased loans and leases | Real estate – commercial mortgage: | Owner-occupied
Summary of loans
Gross loans	1,344,154	1,334,765
Non purchased loans and leases | Real estate – commercial mortgage: | Non-owner occupied
Summary of loans
Gross loans	2,221,206	2,194,739
Non purchased loans and leases | Installment loans to individuals
Summary of loans
Gross loans	$ 121,136	$ 149,862