v3.26.1
Derivatives and Hedging Activities - Schedule of Fair Value Hedge Accounting on Carrying Value of Hedged Items (Details) - USD ($)
 12 Months Ended
Sep. 30, 2025
Jun. 30, 2026
Derivatives, Fair Value [Line Items]    
Carrying value of hedged items $ 6,366,196,000 $ 5,886,037,000
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items 22,246,000 (4,464,000)
Mortgage loan fair value hedges    
Derivatives, Fair Value [Line Items]    
Portfolio layer method, amortized cost 5,393,257,000 5,003,997,000
Portfolio layer method, cumulative adjustment, increase (decrease) 8,262,000 (6,486,000)
Amortized cost, designated in portfolio hedging relationship 1,570,000,000 1,370,000,000
Hedged asset, discontinued 1,600,000,000  
Hedged asset, discontinued fair value 4,016,668  
Commercial loan fair value hedges    
Derivatives, Fair Value [Line Items]    
Carrying value of hedged items 32,829,000  
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items (1,468,000)  
Mortgage backed securities fair value hedges    
Derivatives, Fair Value [Line Items]    
Carrying value of hedged items 940,110,000 882,040,000
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items 15,452,000 2,022,000
Amortized cost, designated in portfolio hedging relationship 610,000,000 610,000,000
Location, Statement of Financial Position, Balance [Axis]: us-gaap:DebtSecuritiesAvailableForSaleExcludingAccruedInterest    
Derivatives, Fair Value [Line Items]    
Carrying value of hedged items $ 940,110,000 $ 882,040,000
Hedged Liability, Statement of Financial Position [Extensible Enumeration] Available-for-sale securities, at fair value Available-for-sale securities, at fair value
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items $ 15,452,000 $ 2,022,000
Location, Statement of Financial Position, Balance [Axis]: us-gaap:FinancingReceivableExcludingAccruedInterestAfterAllowanceForCreditLoss    
Derivatives, Fair Value [Line Items]    
Carrying value of hedged items $ 5,426,086,000 $ 5,003,997,000
Hedged Liability, Statement of Financial Position [Extensible Enumeration] Net loans Net loans
Cumulative gain (loss) fair value hedge adjustment included in carrying amount of hedged items $ 6,794,000 $ (6,486,000)