Allowance for Credit Losses - Summary of Total Non Purchased and Purchased Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	$ 10,153,267		$ 10,937,807
Unearned income	(4,025)		(4,160)
Loans, net of unearned income	10,149,242		10,933,647	$ 10,997,304
Allowance for credit losses	(172,354)	$ (173,106)	(176,144)	(145,387)	$ (120,185)	$ (52,162)
Loans, net	9,976,888		10,757,503
Commercial, financial, agricultural
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,634,633		2,536,984
Loans, net of unearned income	1,634,633			2,641,598
Allowance for credit losses	(36,994)	(37,592)	(39,031)	(30,685)	(25,937)	(10,658)
Lease financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	78,028		80,022
Loans, net of unearned income	74,003			80,779
Allowance for credit losses	(1,511)	(1,546)	(1,624)	(1,812)		(910)	$ (1,588)
Real estate – construction:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,051,359		858,104
Loans, net of unearned income	1,051,359			791,108
Allowance for credit losses	(15,729)	(14,977)	(16,047)	(12,538)	(10,924)	(5,029)
Real estate – construction: | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	277,163		246,673
Real estate – construction: | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	774,196		611,431
Real estate – 1-4 family mortgage:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	2,702,091		2,698,308
Loans, net of unearned income	2,702,091			2,788,513
Allowance for credit losses	(31,303)	(31,694)	(32,165)	(29,401)	(27,320)	(9,814)
Real estate – 1-4 family mortgage: | Primary
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,790,522		1,750,951
Real estate – 1-4 family mortgage: | Home equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	489,933		513,160
Real estate – 1-4 family mortgage: | Rental/investment
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	297,341		296,364
Real estate – 1-4 family mortgage: | Land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	124,295		137,833
Real estate – commercial mortgage:
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	4,530,169		4,554,852
Loans, net of unearned income	4,530,169			4,410,753
Allowance for credit losses	(74,893)	(76,225)	(76,127)	(60,061)	(44,237)	(24,990)
Real estate – commercial mortgage: | Land development
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	124,949		149,579
Real estate – commercial mortgage: | Owner-occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	1,663,191		1,657,806
Real estate – commercial mortgage: | Non-owner occupied
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	2,742,029		2,747,467
Installment loans to individuals
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gross loans	156,987		209,537
Loans, net of unearned income	156,987			284,553
Allowance for credit losses	$ (11,924)	$ (11,072)	$ (11,150)	$ (10,890)	$ (10,179)	$ (761)