Loans and Leases and the Allowance for Credit Losses - Summary of Payment Status of Loans Modified (Detail) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	$ 1,247,000	$ 1,198,000
Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	986,000	1,114,000
30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	211,000	56,000
Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	50,000	28,000
Commercial and industrial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	317,000	127,000
Commercial and industrial | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	308,000	109,000
Commercial and industrial | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	5,000	4,000
Commercial and industrial | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	4,000	14,000
Commercial Real Estate | Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	515,000	423,000
Commercial Real Estate | Commercial | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	422,000	406,000
Commercial Real Estate | Commercial | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	84,000	17,000
Commercial Real Estate | Commercial | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	9,000	0
Commercial Real Estate | Residential builder and developer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	14,000	71,000
Commercial Real Estate | Residential builder and developer | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	13,000	71,000
Commercial Real Estate | Residential builder and developer | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	1,000	0
Commercial Real Estate | Residential builder and developer | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Commercial Real Estate | Other commercial construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	215,000	440,000
Commercial Real Estate | Other commercial construction | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	141,000	440,000
Commercial Real Estate | Other commercial construction | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	74,000	0
Commercial Real Estate | Other commercial construction | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Residential Real Estate | Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	175,000	125,000
Residential Real Estate | Residential | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	93,000	79,000
Residential Real Estate | Residential | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	45,000	34,000
Residential Real Estate | Residential | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	37,000	12,000
Residential Real Estate | Residential — limited documentation
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	8,000	11,000
Residential Real Estate | Residential — limited documentation | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	6,000	8,000
Residential Real Estate | Residential — limited documentation | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	2,000	1,000
Residential Real Estate | Residential — limited documentation | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	2,000
Consumer: | Home equity lines and loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	2,000	1,000
Consumer: | Home equity lines and loans | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	2,000	1,000
Consumer: | Home equity lines and loans | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Home equity lines and loans | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Recreational finance
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	1,000	0
Consumer: | Recreational finance | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	1,000	0
Consumer: | Recreational finance | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Recreational finance | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Automobile
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Automobile | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Automobile | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Automobile | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Other | Current
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Other | 30-89 Days Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	0	0
Consumer: | Other | Accruing Loans Past Due 90 Days or More
Accounts, Notes, Loans and Financing Receivable [Line Items]
Amortized cost	$ 0	$ 0