Allowance for Credit Losses - Summary of Total Non Purchased and Purchased Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
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
Allowance for credit losses	(170,038)	$ (172,354)	(176,144)	(168,098)	$ (145,387)	$ (52,162)
Loans, net	9,846,786		10,757,503
Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,436,019		2,536,984
Loans, net of unearned income	1,436,019			2,648,062
Allowance for credit losses	(34,977)	(36,994)	(39,031)	(38,195)	(30,685)	(10,658)
Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	83,496		80,022
Loans, net of unearned income	79,215			82,928
Allowance for credit losses	(1,570)	(1,511)	(1,624)	(1,832)	(1,812)	(910)
Real estate – construction:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,091,296		858,104
Loans, net of unearned income	1,091,296			773,119
Allowance for credit losses	(16,169)	(15,729)	(16,047)	(13,819)	(12,538)	(5,029)
Real estate – construction: | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	307,825		246,673
Real estate – construction: | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	783,471		611,431
Real estate – 1-4 family mortgage:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	2,724,743		2,698,308
Loans, net of unearned income	2,724,743			2,760,394
Allowance for credit losses	(32,181)	(31,303)	(32,165)	(32,705)	(29,401)	(9,814)
Real estate – 1-4 family mortgage: | Primary
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,808,139		1,750,951
Real estate – 1-4 family mortgage: | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	481,552		513,160
Real estate – 1-4 family mortgage: | Rental/investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	291,116		296,364
Real estate – 1-4 family mortgage: | Land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	143,936		137,833
Real estate – commercial mortgage:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	4,535,730		4,554,852
Loans, net of unearned income	4,535,730			4,577,009
Allowance for credit losses	(73,895)	(74,893)	(76,127)	(70,582)	(60,061)	(24,990)
Real estate – commercial mortgage: | Land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	126,266		149,579
Real estate – commercial mortgage: | Owner-occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,630,227		1,657,806
Real estate – commercial mortgage: | Non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	2,779,237		2,747,467
Installment loans to individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	149,821		209,537
Loans, net of unearned income	149,821			243,226
Allowance for credit losses	$ (11,246)	$ (11,924)	$ (11,150)	$ (10,965)	$ (10,890)	$ (761)