Loans Held for Investment and Allowance for Credit Losses on Loans - Collateral-dependent Gross Loans Held for Investment by Collateral Type and Related Specific Allocation (Detail) - USD ($)
$ in Thousands

Loans Held for Investment and Allowance for Credit Losses on Loans - Collateral-dependent Gross Loans Held for Investment by Collateral Type and Related Specific Allocation (Detail) - USD ($) $ in Thousands	Sep. 30, 2025	Jun. 30, 2025	Dec. 31, 2024	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	$ 8,278,247		$ 8,025,110	$ 8,180,361
Specific Allocation	99,511	$ 96,988	99,497	101,882	$ 99,626	$ 96,800
Real Estate Asset [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	9,301		30,222
Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	9,893		10,197
Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	636		520
Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	4,504		7,988
Collateral Pledged [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	19,830		40,939
Real Estate [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	937,976		931,709
Specific Allocation	7,531	7,248	6,869	7,408	7,370	7,483
Real Estate [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,703,037		1,578,483
Specific Allocation	35,479	35,217	33,097	33,746	33,867	33,080
Real Estate [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	661,882		756,662
Specific Allocation	4,830	4,907	8,671	8,355	6,780	3,950
Real Estate [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	249,539		250,373
Specific Allocation	2,527	2,265	2,336	3,341	3,519	3,414
Real Estate [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,486,440		1,431,265
Specific Allocation	4,769	4,645	4,568	5,646	5,572	4,914
Real Estate [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	305,294		275,461
Specific Allocation	2,007	1,821	1,741	1,737	1,729	1,646
Real Estate [Member] \| Real Estate Asset [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	4,445
Real Estate [Member] \| Real Estate Asset [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	2,473		7,890
Real Estate [Member] \| Real Estate Asset [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	859		20,142
Real Estate [Member] \| Real Estate Asset [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	829		206
Real Estate [Member] \| Real Estate Asset [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	410		300
Real Estate [Member] \| Real Estate Asset [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	207		100
Real Estate [Member] \| Real Estate Asset [Member] \| Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	78		1,584
Real Estate [Member] \| Business Assets [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	551
Real Estate [Member] \| Business Assets [Member] \| Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	164		110
Real Estate [Member] \| Other Assets [Member] \| Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	12		13
Real Estate [Member] \| Specific Allocation [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	585
Real Estate [Member] \| Specific Allocation [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	644		879
Real Estate [Member] \| Specific Allocation [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	251		3,755
Real Estate [Member] \| Specific Allocation [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	229		75
Real Estate [Member] \| Specific Allocation [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	160		93
Real Estate [Member] \| Specific Allocation [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	147		34
Real Estate [Member] \| Specific Allocation [Member] \| Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	124		688
Real Estate [Member] \| Collateral Pledged [Member] \| Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	4,996
Real Estate [Member] \| Collateral Pledged [Member] \| Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	2,473		7,890
Real Estate [Member] \| Collateral Pledged [Member] \| Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	859		20,142
Real Estate [Member] \| Collateral Pledged [Member] \| Construction Residential Real Estate Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	829		206
Real Estate [Member] \| Collateral Pledged [Member] \| Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	410		300
Real Estate [Member] \| Collateral Pledged [Member] \| Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	207		100
Real Estate [Member] \| Collateral Pledged [Member] \| Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	254		1,707
Commercial Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,458,122		1,363,462
Specific Allocation	24,889	24,047	24,150	22,260	21,475	22,745
Commercial Non-real Estate [Member] \| Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	8,089		10,087
Commercial Non-real Estate [Member] \| Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	0		108
Commercial Non-real Estate [Member] \| Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	1,978		2,222
Commercial Non-real Estate [Member] \| Collateral Pledged [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	8,089		10,195
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	493,900		478,647
Specific Allocation	5,097	4,837	4,833	4,380	4,383	4,401
Consumer Non-real Estate [Member] \| Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	624		399
Consumer Non-real Estate [Member] \| Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	276		242
Consumer Non-real Estate [Member] \| Collateral Pledged [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	624		399
Oil and Gas [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	536,527		509,858
Specific Allocation	7,256	$ 6,870	$ 7,536	$ 9,092	$ 9,014	$ 9,030
Oil and Gas [Member] \| Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,089
Oil and Gas [Member] \| Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	110
Oil and Gas [Member] \| Collateral Pledged [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	$ 1,089