Acquisitions - Narrative (Details)					12 Months Ended
	Nov. 19, 2021 USD ($) loan shares	Oct. 08, 2021 USD ($) branch shares	Oct. 31, 2019 USD ($) $ / shares shares	Apr. 12, 2019 USD ($) shares	Dec. 31, 2019 USD ($)	Dec. 31, 2021 USD ($) center	Nov. 17, 2021 $ / shares	Dec. 31, 2020 USD ($) $ / shares shares	Oct. 30, 2019 USD ($) branch	Oct. 29, 2019 $ / shares shares	Apr. 11, 2019 USD ($) branch	Feb. 27, 2009 $ / shares shares
Business Acquisition [Line Items]
Goodwill						$ 1,146,007,000		$ 1,075,305,000
Preferred stock, par value (in dollars per share) | $ / shares								$ 0.01				$ 0.01
Number of financial centers | center						199
Preferred stock, shares authorized (in shares) | shares								40,040,000				40,040,000
Preferred stock, shares issued (in shares) | shares								767
Landmark Community Bank
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares		4,499,872
Payments to acquire businesses, gross		$ 138,200,000
Stock issued for acquisition		$ 6,451,727,430
Number of bank branches acquired | branch		8
Assets acquired		$ 968,500,000	$ 968,493,000						$ 966,006,000
Loans acquired		789,300,000	789,318,000						785,551,000
Deposits acquired		802,700,000	802,671,000						803,005,000
Goodwill		$ 31,700,000	31,733,000
Triumph Bancshares, Inc.
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares		4,164,712
Payments to acquire businesses, gross		$ 127,900,000
Stock issued for acquisition		$ 1,693,402,930
Number of bank branches acquired | branch		6
Assets acquired		$ 848,200,000	848,201,000						845,523,000
Loans acquired		700,400,000	700,440,000						702,460,000
Deposits acquired		719,700,000	719,734,000						718,640,000
Goodwill		$ 39,000,000	$ 38,968,000
Landrum Company
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares			17,349,722
Stock issued for acquisition					$ 415,772,000
Assets acquired			$ 3,399,152,000						3,381,889,000
Loans acquired			2,005,486,000						2,049,137,000
Deposits acquired			3,049,600,000						$ 3,049,301,000
Goodwill			$ 151,125,000		131,300,000
Number of financial centers | branch									39
Reliance Bancshares, Inc.
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares				3,999,623
Payments to acquire businesses, gross				$ 62,700,000
Stock issued for acquisition				42,000,000	144,830,000
Assets acquired				1,534,312,000							$ 1,549,954,000
Loans acquired				1,096,870,000							1,138,527,000
Deposits acquired				1,225,267,000							$ 1,227,058,000
Goodwill				$ 78,493,000	$ 78,500,000
Number of financial centers | branch											22
Spirit of Texas Bancshares, Inc.
Business Acquisition [Line Items]
Equity interest issued or issuable (in shares) | shares	18,325,000
Payments to acquire businesses, gross	$ 581,000,000
Number of bank branches acquired | loan	37
Assets acquired	$ 3,300,000,000
Loans acquired	2,300,000,000
Deposits acquired	$ 2,800,000,000
Closing price of common stock (in dollars per share) | $ / shares							$ 31.73
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]
Share received from merger (in shares) | 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