Securities (Schedule Of Contractual Maturities) (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Sep. 30, 2021
Marketable Securities [Abstract]
Available-for-sale Securities, One year or less, Amortized Cost	$ 210
Available-for-sale Securities, One year through five years, Amortized Cost	519,976
Available-for-sale Securities, Five years through ten years, Amortized Cost	4,000
Available-for-sale Securities, Included in maturity categories, Amortized Cost	524,186
MBS, Amortized Cost	1,306,076
Available-for-sale Securities, Amortized Cost	1,830,262	$ 2,008,456
Available-for-sale Securities, One year or less, Estimated Fair Value	210
Available-for-sale Securities, One year through five years, Estimated Fair Value	483,193
Available-for-sale Securities, Five years through ten years, Estimated Fair Value	4,010
Available-for-sale Securities, Included in maturity categories, Estimated Fair Value	487,413
MBS, Estimated Fair Value	1,206,747
Available-for-sale Securities, Estimated Fair Value	$ 1,694,160	$ 2,014,608

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in sixth through tenth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amortized cost excluding accrued interest, after allowance for credit loss, 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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