Acquisitions - Textual (Details) $ / shares in Units, $ in Thousands			9 Months Ended
	Oct. 31, 2019 USD ($) $ / shares shares	Apr. 12, 2019 USD ($) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) financial_center $ / shares shares	Dec. 31, 2019 USD ($) $ / shares shares	Oct. 30, 2019 USD ($) financial_center	Oct. 29, 2019 $ / shares shares	Apr. 11, 2019 USD ($) financial_center	Feb. 12, 2019 shares	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				226
Goodwill				$ 1,075,305	$ 1,055,520
Stock issued for Reliance acquisition – 3,999,623 shares			$ 144,830
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
Preferred stock, shares outstanding (in shares) | shares				767	767
Landrum Company
Business Acquisition [Line Items]
Shares issued (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	$ 407
Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Shares issued (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 Reliance acquisition – 3,999,623 shares		$ 42,000
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]
Shares issued, 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
Shares issued, 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]
Shares issued (in shares) | shares	767
Series A or B Preferred Stock | Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Shares issued, conversion ratio (in shares)		1
Series C Preferred Stock | Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Shares issued, conversion ratio (in shares)		1
Preferred stock, shares authorized (in shares) | shares							140		140
Preferred stock, shares issued (in shares) | shares							0
Preferred stock, shares outstanding (in shares) | shares							0