Purchased Loans - Summary of Purchased Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Summary of loans
Gross loans	$ 10,016,824	$ 10,933,647	$ 11,084,738
Commercial, financial, agricultural
Summary of loans
Gross loans	1,436,019		2,648,062
Real estate – construction:
Summary of loans
Gross loans	1,091,296		773,119
Real estate – 1-4 family mortgage:
Summary of loans
Gross loans	2,724,743		2,760,394
Real estate – commercial mortgage:
Summary of loans
Gross loans	4,535,730		4,577,009
Installment loans to individuals
Summary of loans
Gross loans	149,821		$ 243,226
Purchased loans
Summary of loans
Gross loans	1,140,944	1,514,107
Purchased loans | Commercial, financial, agricultural
Summary of loans
Gross loans	114,450	176,513
Purchased loans | Real estate – construction:
Summary of loans
Gross loans	4,993	30,952
Purchased loans | Real estate – construction: | Residential
Summary of loans
Gross loans	1,288	2,859
Purchased loans | Real estate – construction: | Commercial
Summary of loans
Gross loans	3,705	28,093
Purchased loans | Real estate – 1-4 family mortgage:
Summary of loans
Gross loans	240,347	341,744
Purchased loans | Real estate – 1-4 family mortgage: | Primary
Summary of loans
Gross loans	150,944	214,770
Purchased loans | Real estate – 1-4 family mortgage: | Home equity
Summary of loans
Gross loans	56,692	80,392
Purchased loans | Real estate – 1-4 family mortgage: | Rental/investment
Summary of loans
Gross loans	22,507	31,928
Purchased loans | Real estate – 1-4 family mortgage: | Land development
Summary of loans
Gross loans	10,204	14,654
Purchased loans | Real estate – commercial mortgage:
Summary of loans
Gross loans	740,832	905,223
Purchased loans | Real estate – commercial mortgage: | Land development
Summary of loans
Gross loans	19,791	29,454
Purchased loans | Real estate – commercial mortgage: | Owner-occupied
Summary of loans
Gross loans	264,939	323,041
Purchased loans | Real estate – commercial mortgage: | Non-owner occupied
Summary of loans
Gross loans	456,102	552,728
Purchased loans | Real estate – commercial mortgage: | Land development
Summary of loans
Gross loans	19,791	29,454
Purchased loans | Installment loans to individuals
Summary of loans
Gross loans	$ 40,322	$ 59,675