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	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	$ 8,114,488		$ 8,025,110	$ 8,047,448
Specific Allocation	96,988	$ 100,455	99,497	99,626	$ 97,267	$ 96,800
Real Estate Asset [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	6,564		30,222
Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	8,983		10,197
Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	588		520
Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	3,995		7,988
Collateral Pledged [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	16,135		40,939
Real Estate [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	937,426		931,709
Specific Allocation	7,248	6,991	6,869	7,370	7,468	7,483
Real Estate [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,674,229		1,578,483
Specific Allocation	35,217	33,753	33,097	33,867	33,180	33,080
Real Estate [Member] | Construction and Development Less than 60 Months [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	684,291		756,662
Specific Allocation	4,907	8,613	8,671	6,780	6,596	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	235,032		250,373
Specific Allocation	2,265	2,282	2,336	3,519	3,464	3,414
Real Estate [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,462,758		1,431,265
Specific Allocation	4,645	4,666	4,568	5,572	4,923	4,914
Real Estate [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	291,362		275,461
Specific Allocation	1,821	1,790	1,741	1,729	1,652	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	1,399
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	3,652		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	800		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	206		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	333		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	95		100
Real Estate [Member] | Real Estate Asset [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	79		1,584
Real Estate [Member] | Business Assets [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	110		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	283
Real Estate [Member] | Specific Allocation [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	1,031		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	225		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	75		75
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	99		93
Real Estate [Member] | Specific Allocation [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	32		34
Real Estate [Member] | Specific Allocation [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	98		688
Real Estate [Member] | Collateral Pledged [Member] | Commercial Real Estate Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,399
Real Estate [Member] | Collateral Pledged [Member] | Commercial Real Estate Non-Owner Occupied [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	3,652		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	800		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	206		206
Real Estate [Member] | Collateral Pledged [Member] | Residential Real Estate First Lien [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	333		300
Real Estate [Member] | Collateral Pledged [Member] | Residential Real Estate All Other [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	95		100
Real Estate [Member] | Collateral Pledged [Member] | Agriculture [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	201		1,707
Commercial Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,427,576		1,363,462
Specific Allocation	24,047	23,877	24,150	21,475	20,482	22,745
Commercial Non-real Estate [Member] | Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	7,762		10,087
Commercial Non-real Estate [Member] | Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	25		108
Commercial Non-real Estate [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	1,764		2,222
Commercial Non-real Estate [Member] | Collateral Pledged [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	7,787		10,195
Consumer Non-real Estate [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	481,725		478,647
Specific Allocation	4,837	4,820	4,833	4,383	4,335	4,401
Consumer Non-real Estate [Member] | Other Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	551		399
Consumer Non-real Estate [Member] | Specific Allocation [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Specific Allocation	278		242
Consumer Non-real Estate [Member] | Collateral Pledged [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	551		399
Oil and Gas [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	472,105		509,858
Specific Allocation	6,870	$ 7,887	$ 7,536	$ 9,014	$ 9,030	$ 9,030
Oil and Gas [Member] | Business Assets [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Collateral Dependent Loans	1,111
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	$ 1,111