v3.26.1
Derivatives and Hedging Activities - Schedule of Fair Value, Notional Amount and Balance Sheet Classification (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Sep. 30, 2025
Location, Statement of Financial Position, Balance [Axis]: us-gaap:AccountsPayableAndOtherAccruedLiabilities    
Derivatives, Fair Value [Line Items]    
Notional amount $ 2,059,875 $ 2,687,017
Derivative liabilities, fair value 43,640 73,330
Location, Statement of Financial Position, Balance [Axis]: us-gaap:AccountsPayableAndOtherAccruedLiabilities | Interest rate contracts    
Derivatives, Fair Value [Line Items]    
Notional amount 959,875 977,017
Derivative liabilities, fair value 37,088 37,818
Location, Statement of Financial Position, Balance [Axis]: us-gaap:AccountsPayableAndOtherAccruedLiabilities | Commercial loan fair value hedges    
Derivatives, Fair Value [Line Items]    
Notional amount   0
Derivative liabilities, fair value   0
Location, Statement of Financial Position, Balance [Axis]: us-gaap:AccountsPayableAndOtherAccruedLiabilities | Mortgage loan fair value hedges    
Derivatives, Fair Value [Line Items]    
Notional amount 700,000 1,100,000
Derivative liabilities, fair value 2,825 20,426
Location, Statement of Financial Position, Balance [Axis]: us-gaap:AccountsPayableAndOtherAccruedLiabilities | Mortgage backed securities fair value hedges    
Derivatives, Fair Value [Line Items]    
Notional amount 400,000 610,000
Derivative liabilities, fair value 3,727 15,086
Location, Statement of Financial Position, Balance [Axis]: us-gaap:AccountsPayableAndOtherAccruedLiabilities | Borrowings cash flow hedges    
Derivatives, Fair Value [Line Items]    
Notional amount 0 0
Derivative liabilities, fair value 0 0
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssets    
Derivatives, Fair Value [Line Items]    
Notional amount 3,189,875 2,381,358
Derivative assets, fair value 153,436 151,271
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssets | Interest rate contracts    
Derivatives, Fair Value [Line Items]    
Notional amount 959,875 977,017
Derivative assets, fair value 37,009 37,347
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssets | Commercial loan fair value hedges    
Derivatives, Fair Value [Line Items]    
Notional amount   34,341
Derivative assets, fair value   1,611
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssets | Mortgage loan fair value hedges    
Derivatives, Fair Value [Line Items]    
Notional amount 670,000 470,000
Derivative assets, fair value 10,034 13,082
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssets | Mortgage backed securities fair value hedges    
Derivatives, Fair Value [Line Items]    
Notional amount 210,000 0
Derivative assets, fair value 1,947 0
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssets | Borrowings cash flow hedges    
Derivatives, Fair Value [Line Items]    
Notional amount 1,350,000 900,000
Derivative assets, fair value $ 104,446 $ 99,231