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Derivatives and Hedging Activities - Impact of Derivative Instruments on AOCI (Details) - Pay fixed/receive floating swaps on borrowings cash flow hedges - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Derivative [Line Items]
Pay fixed/receive floating swaps on borrowings cash flow hedges	$ 70,565	$ (12,428)	$ 90,683	$ (9,313)
Reclassification adjustment of net (gain)/loss included in net income	(14,110)	0	(14,110)	0
Total pre-tax gain/(loss) recognized in AOCI	$ 56,455	$ (12,428)	$ 76,573	$ (9,313)

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Amount, before tax and after reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
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Amount, before tax and reclassification, of gain (loss) from derivative instrument designated and qualifying cash flow hedge included in assessment of hedge effectiveness.

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Amount, before tax, of reclassification of gain (loss) from accumulated other comprehensive income (AOCI) for derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

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