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, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Derivative [Line Items]
Pay fixed/receive floating swaps on borrowings cash flow hedges	$ 56,323	$ 70,565	$ 62,769	$ 90,683
Reclassification adjustment of net (gain)/loss included in net income	0	(14,110)	0	(14,110)
Total pre-tax gain/(loss) recognized in AOCI	$ 56,323	$ 56,455	$ 62,769	$ 76,573