Derivatives and Hedging Activities - Impact of Derivative Instruments on AOCI (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Derivative [Line Items]
Total pre-tax gain/(loss) recognized in AOCI	$ (12,428)	$ (6,150)	$ (9,313)	$ (16,650)
Pay fixed/receive floating swaps on borrowings cash flow hedges
Derivative [Line Items]
Total pre-tax gain/(loss) recognized in AOCI	$ (12,428)	$ (6,150)	$ (9,313)	$ (16,650)