Fair Value Of Financial Instruments (Schedule Of Fair Value Assets Measured On A Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Sep. 30, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	$ 829,704	$ 867,216
Interest rate swap	765	926
MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	825,961	863,500
Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	3,743	3,716
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	829,704	867,216
Interest rate swap	765	926
Assets	830,469	868,142
Fair Value, Recurring [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	0
Interest rate swap	0	0
Assets	0	0
Fair Value, Recurring [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	829,704	867,216
Interest rate swap	765	926
Assets	830,469	868,142
Fair Value, Recurring [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	0
Interest rate swap	0	0
Assets	0	0
Fair Value, Recurring [Member] \| MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	825,961	863,500
Fair Value, Recurring [Member] \| MBS [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	0
Fair Value, Recurring [Member] \| MBS [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	825,961	863,500
Fair Value, Recurring [Member] \| MBS [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	0
Fair Value, Recurring [Member] \| Corporate Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	3,743	3,716
Fair Value, Recurring [Member] \| Corporate Bonds [Member] \| Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	0	0
Fair Value, Recurring [Member] \| Corporate Bonds [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	3,743	3,716
Fair Value, Recurring [Member] \| Corporate Bonds [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	$ 0	$ 0

Capitol Federal Financial, Inc. 10-Q