Loans and Allowance for Credit Losses - Summary of Aging Analysis of Modifications (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	$ 34,758	$ 22,918
Current | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	27,176	20,801
30-59 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	7,475	1,610
60-89 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	62
90+ Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	107	445
Commercial Loans | Commercial real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	12,482	13,505
Commercial Loans | Commercial real estate | Current | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	12,482	13,505
Commercial Loans | Commercial real estate | 30-59 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	0
Commercial Loans | Commercial real estate | 60-89 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	0
Commercial Loans | Commercial real estate | 90+ Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	0
Commercial Loans | Commercial and industrial
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	21,839	6,892
Commercial Loans | Commercial and industrial | Current | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	14,364	6,447
Commercial Loans | Commercial and industrial | 30-59 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	7,475	0
Commercial Loans | Commercial and industrial | 60-89 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	0
Commercial Loans | Commercial and industrial | 90+ Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	445
Commercial Loans | Commercial construction
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months		1,610
Commercial Loans | Commercial construction | Current | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months		0
Commercial Loans | Commercial construction | 30-59 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months		1,610
Commercial Loans | Commercial construction | 60-89 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months		0
Commercial Loans | Commercial construction | 90+ Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months		0
Business banking
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	107	658
Business banking | Current | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	107	658
Business banking | 30-59 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	0
Business banking | 60-89 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	0
Business banking | 90+ Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	0
Consumer Loans | Consumer real estate
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	330	253
Consumer Loans | Consumer real estate | Current | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	223	191
Consumer Loans | Consumer real estate | 30-59 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	0
Consumer Loans | Consumer real estate | 60-89 Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	0	62
Consumer Loans | Consumer real estate | 90+ Days Past Due | Accrual
Financing Receivable, Troubled Debt Restructuring [Line Items]
Financing receivable, modified, after 12 months	$ 107	$ 0