Purchased Loans - Summary of Purchased Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020
Summary of loans
Gross loans	$ 10,688,408	$ 10,933,647	$ 9,769,377
Commercial, financial, agricultural
Summary of loans
Gross loans	2,249,287		1,424,576
Real estate – construction:
Summary of loans
Gross loans	955,918		787,895
Real estate – 1-4 family mortgage
Summary of loans
Gross loans	2,686,061		2,846,301
Real estate – commercial mortgage:
Summary of loans
Gross loans	4,549,027		4,308,708
Installment loans to individuals
Summary of loans
Gross loans	172,859		$ 317,218
Purchased loans
Summary of loans
Gross loans	1,395,906	1,514,107
Purchased loans | Commercial, financial, agricultural
Summary of loans
Gross loans	143,843	176,513
Purchased loans | Real estate – construction:
Summary of loans
Gross loans	22,332	30,952
Purchased loans | Real estate – construction: | Residential
Summary of loans
Gross loans	2,561	2,859
Purchased loans | Real estate – construction: | Commercial
Summary of loans
Gross loans	19,771	28,093
Purchased loans | Real estate – 1-4 family mortgage
Summary of loans
Gross loans	305,141	341,744
Purchased loans | Real estate – 1-4 family mortgage | Primary
Summary of loans
Gross loans	190,539	214,770
Purchased loans | Real estate – 1-4 family mortgage | Home equity
Summary of loans
Gross loans	72,413	80,392
Purchased loans | Real estate – 1-4 family mortgage | Rental/investment
Summary of loans
Gross loans	28,800	31,928
Purchased loans | Real estate – 1-4 family mortgage | Land development
Summary of loans
Gross loans	13,389	14,654
Purchased loans | Real estate – commercial mortgage:
Summary of loans
Gross loans	872,867	905,223
Purchased loans | Real estate – commercial mortgage: | Land development
Summary of loans
Gross loans	25,588	29,454
Purchased loans | Real estate – commercial mortgage: | Owner-occupied
Summary of loans
Gross loans	300,616	323,041
Purchased loans | Real estate – commercial mortgage: | Non-owner occupied
Summary of loans
Gross loans	546,663	552,728
Purchased loans | Real estate – commercial mortgage: | Land development
Summary of loans
Gross loans	25,588	29,454
Purchased loans | Installment loans to individuals
Summary of loans
Gross loans	$ 51,723	$ 59,675