Fair Value Of Financial Instruments (Schedule Of Fair Value Assets Measured On A Recurring Basis) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	$ 2,015,705
AFS securities		$ 1,560,950
MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	1,519,028
AFS securities		1,180,803
GSE Debentures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	491,515
AFS securities		370,340
Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	5,162
AFS securities		9,807
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	2,015,705
AFS securities		1,560,950
Interest rate swaps	30,391	53,149
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
AFS securities		0
Interest rate swaps	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	2,015,705
AFS securities		1,560,950
Interest rate swaps	30,391	53,149
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
AFS securities		0
Interest rate swaps	0	0
Fair Value, Recurring [Member] \| MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	1,519,028
AFS securities		1,180,803
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
AFS securities		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	1,519,028
AFS securities		1,180,803
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
AFS securities		0
Fair Value, Recurring [Member] \| GSE Debentures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	491,515
AFS securities		370,340
Fair Value, Recurring [Member] \| GSE Debentures [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
AFS securities		0
Fair Value, Recurring [Member] \| GSE Debentures [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	491,515
AFS securities		370,340
Fair Value, Recurring [Member] \| GSE Debentures [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	0
AFS securities		0
Fair Value, Recurring [Member] \| Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	5,162
AFS securities		9,807
Fair Value, Recurring [Member] \| Municipal 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
AFS securities		0
Fair Value, Recurring [Member] \| Municipal Bonds [Member] \| Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	5,162
AFS securities		9,807
Fair Value, Recurring [Member] \| Municipal Bonds [Member] \| Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS Securities	$ 0
AFS securities		$ 0

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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