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Derivatives and Hedging Activities - Impact of Client Swap Program that are Not Designated in Accounting Hedges (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Client swap program hedges
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ 0	$ 0	$ 0	$ 0
Other noninterest income | Pay fixed/receive floating swap
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	40,929	(28,184)	53,305	(22,776)
Other noninterest income | Receive fixed/pay floating swap
Derivative [Line Items]
Derivative instruments not designated as hedging instruments, gain (loss), net	$ (40,929)	$ 28,184	$ (53,305)	$ 22,776

X

- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5624171-113959

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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