Loans Held for Investment (LHFI) and Allowance for Loan Losses, LHFI - Aging Analysis of Past Due and Nonaccrual LHFI by Loan Type (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	$ 10,174,899	$ 9,824,524
Total LHFI	10,174,899	9,824,524
Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	8,272	9,615
Past Due 60 to 89 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,542	5,304
Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	21,793	9,552
Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	31,607	24,471
Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	10,143,292	9,800,053
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total LHFI	559,804	514,056
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,045	339
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	155	34
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	4,847	161
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	6,047	534
Construction, Land Development and Other Land [Member] | Loans Secured by Real Estate [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	553,757	513,522
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total LHFI	509,195	524,732
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,965	1,505
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	463	523
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	381	896
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	2,809	2,924
Other Secured by 1-4 Family Residential Properties [Member] | Loans Secured by Real Estate [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	506,386	521,808
Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total LHFI	1,382,097	1,216,400
Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	2,624	3,291
Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	612	1,289
Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	5,927	5,110
Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	9,163	9,690
Secured by 1-4 Family Residential Properties [Member] | Other Loans Secured by Real Estate [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,372,934	1,206,710
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	2,924,953	2,709,026
Total LHFI	2,924,953	2,709,026
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	124	920
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,564	972
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,688	1,892
Secured by Nonfarm, Nonresidential Properties [Member] | Loans Secured by Real Estate [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	2,923,265	2,707,134
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total LHFI	986,163	1,065,964
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	87	103
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)		101
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	107	107
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	194	311
Other Real Estate Secured [Member] | Loans Secured by Real Estate [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	985,969	1,065,653
Commercial and Industrial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,327,211	1,309,078
Total LHFI	1,327,211	1,309,078
Commercial and Industrial Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,141	271
Commercial and Industrial Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	72	196
Commercial and Industrial Loans [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	3,426	1,543
Commercial and Industrial Loans [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	4,639	2,010
Commercial and Industrial Loans [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,322,572	1,307,068
Other Construction [Member] | Other Loans Secured by Real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Total LHFI	726,809	794,983
Other Construction [Member] | Other Loans Secured by Real Estate [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	726,809	794,983
Consumer Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	160,802	164,386
Total LHFI	160,802	164,386
Consumer Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,172	926
Consumer Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	215	190
Consumer Loans [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	273	240
Consumer Loans [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,660	1,356
Consumer Loans [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	159,142	163,030
State and Other Political Subdivision Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,125,186	1,000,776
Total LHFI	1,125,186	1,000,776
State and Other Political Subdivision Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	19	117
State and Other Political Subdivision Loans [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	177	177
State and Other Political Subdivision Loans [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	196	294
State and Other Political Subdivision Loans [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	1,124,990	1,000,482
Other Commercial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	472,679	525,123
Total LHFI	472,679	525,123
Other Commercial Loans [Member] | Past Due 30 to 59 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	95	2,143
Other Commercial Loans [Member] | Past Due 60 to 89 Days [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	25	2,971
Other Commercial Loans [Member] | Past Due 90 Days or More [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	5,091	346
Other Commercial Loans [Member] | Financial Asset, Past Due [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	5,211	5,460
Other Commercial Loans [Member] | Current Loans
Financing Receivable Allowance For Credit Losses [Line Items]
Loans held for investment (LHFI)	$ 467,468	$ 519,663