Derivatives and Hedging Activities - Impact of Derivative Instruments on AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative [Line Items]
Total pre-tax gain/(loss) recognized in AOCI	$ (8,045)	$ (10,043)	$ (17,358)	$ (26,692)
Pay fixed/receive floating swaps on borrowings cash flow hedges
Derivative [Line Items]
Total pre-tax gain/(loss) recognized in AOCI	$ (8,045)	$ (10,043)	$ (17,358)	$ (26,692)