Loans Held for Investment and Allowance for Credit Losses on Loans - Summary of Loans Held for Investment by Portfolio Segment (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	$ 6,494,340	$ 6,169,442
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	784,619	684,739
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	1,160,506	1,095,324
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	458,859	415,466
Real Estate [Member] | Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	282,027	254,524
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	1,032,732	937,006
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	160,843	161,018
Real Estate [Member] | Farmland [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	276,465	272,179
Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	1,291,627	1,256,487
Consumer Non-real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	419,490	413,370
Oil and Gas [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	427,792	428,908
Other Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Loans held for investment (net of unearned interest)	$ 199,380	$ 250,421