Securities (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
Dec. 31, 2023	Dec. 31, 2022	Sep. 30, 2023
Marketable Securities [Line Items]
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ (740,462)		$ (1,384,482)
Proceeds from sale of AFS securities	1,272,512	$ 0
Gross loss from securities transaction	14,900
Gross gain from securities transaction	1,600
Net loss from securities transactions	13,345	$ 0
Debt Securities, Available-for-Sale, FV of Securities Sold
Marketable Securities [Line Items]
Debt Securities, Available-for-Sale, Excluding Accrued Interest	$ (1,300,000)

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).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
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-Paragraph 1
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Amount of realized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
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Amount of cash inflow from sale 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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