Fair Value Of Financial Instruments (Schedule Of Fair Value Assets Measured On A Recurring Basis) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	$ 1,229,587	$ 1,204,863
GSE Debentures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	275,155	249,954
MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	937,317	936,487
Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	17,115	18,422
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	1,229,587	1,204,863
Interest rate swaps	25,925	33,090
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 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	1,229,587	1,204,863
Interest rate swaps	25,925	33,090
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 swaps	0	0
Fair Value, Recurring [Member] | GSE Debentures [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	937,317	936,487
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	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	937,317	936,487
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	0
Fair Value, Recurring [Member] | MBS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	275,155	249,954
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	275,155	249,954
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] | Municipal Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
AFS securities	17,115	18,422
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	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	17,115	18,422
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	$ 0