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Derivatives and Hedging Activities - Additional Information (Detail)
12 Months Ended
Sep. 30, 2022
USD ($)
Contract
Sep. 30, 2021
USD ($)
Contract
Derivative Instruments And Hedging Activities Disclosures [Line Items]    
Interest income (expense) $ 59,771,000 $ 52,894,000
Derivative liability, collateral against obligations   640,000
Designated as Hedging Instrument [Member] | Cash Flow Hedges of Interest Rate Risk [Member] | Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Member]    
Derivative Instruments And Hedging Activities Disclosures [Line Items]    
Interest income (expense) 823,000 (2,000,000.0)
Increase (decrease) in accrued interest payable $ (8,200,000)  
Designated as Hedging Instrument [Member] | Cash Flow Hedges of Interest Rate Risk [Member] | Interest Rate Swaps [Member] | Variable Rate [Member] | Brokered Deposits [Member]    
Derivative Instruments And Hedging Activities Disclosures [Line Items]    
Derivative, number of instruments | Contract 10  
Derivative, notional principal amount $ 225,000,000  
Designated as Hedging Instrument [Member] | Cash Flow Hedges of Interest Rate Risk [Member] | Interest Rate Swaps [Member] | Variable Rate [Member] | Commercial Loans [Member]    
Derivative Instruments And Hedging Activities Disclosures [Line Items]    
Derivative, notional principal amount $ 191,000,000 $ 175,000,000
Designated as Hedging Instrument [Member] | Cash Flow Hedges of Interest Rate Risk [Member] | Interest Rate Swaps [Member] | Variable Rate [Member] | FHLB Advances [Member] |    
Derivative Instruments And Hedging Activities Disclosures [Line Items]    
Derivative, number of instruments | Contract   11
Derivative, notional principal amount   $ 235,000,000