Acquisitions (Details) $ / shares in Units, $ in Thousands			12 Months Ended
	Oct. 31, 2019 USD ($) $ / shares shares	Apr. 12, 2019 USD ($) shares	Dec. 31, 2019 USD ($) $ / shares shares	Dec. 31, 2020 USD ($) financial_center $ / shares shares	Oct. 30, 2019 USD ($) financial_center	Oct. 29, 2019 $ / shares shares	Apr. 11, 2019 USD ($) financial_center	Feb. 27, 2009 $ / shares shares
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares			$ 0.01	$ 0.01				$ 0.01
Number of financial centers | financial_center				204
Goodwill			$ 1,055,520	$ 1,075,305
Preferred stock, shares authorized (in shares) | shares			40,040,000	40,040,000				40,040,000
Preferred stock, shares issued (in shares) | shares			767	767
Landrum Company
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares	17,349,722
Number of financial centers | financial_center					39
Assets acquired	$ 3,399,152				$ 3,381,889
Loans acquired	2,005,486				2,049,137
Deposits acquired	3,049,600				$ 3,049,301
Goodwill	$ 151,125			$ 131,300
Stock issued for acquisition			$ 415,772
Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares		3,999,623
Number of financial centers | financial_center							22
Assets acquired		$ 1,534,312					$ 1,549,954
Loans acquired		1,096,870					1,138,527
Deposits acquired		1,225,267					$ 1,227,058
Goodwill		78,493		$ 78,500
Payments to acquire businesses, gross		62,700
Stock issued for acquisition		$ 42,000	$ 144,830
Common Class A | Landrum Company
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.01
Preferred Class B | Landrum Company
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.01
Series E Preferred Stock | Landrum Company
Business Acquisition [Line Items]
Equity interest issued or issuable, conversion ratio (in shares)	17,350,000
Series D Preferred Stock | Landrum Company
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares	$ 0.01
Equity interest issued or issuable, conversion ratio (in shares)	1
Series D Preferred Stock | Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares						$ 0.01
Preferred Stock | Landrum Company
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares	767
Series A or B Preferred Stock | Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Equity interest issued or issuable, conversion ratio (in shares)		1
Series C Preferred Stock | Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Equity interest issued or issuable, conversion ratio (in shares)		1
Preferred stock, shares authorized (in shares) | shares						140
Preferred stock, shares issued (in shares) | shares						0