Borrowed Funds (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023	Sep. 30, 2023
FHLB Advances, Fixed Rate	$ 1,990,000		$ 1,990,000		$ 2,020,000
FHLB Advances, Variable Rate	300,000		300,000		365,000
Finance Lease, Liability	1,100		1,100
Repayments on borrowings			864,864	$ 3,441,124
Interest rate swaps, notional amount	300,000		$ 300,000		$ 365,000
Interest rate swaps, remaining term to maturity			1 year 8 months 12 days		2 years 1 month 6 days
Interest rate swaps, fair value	$ 6,600		$ 6,600		$ 13,000
Derivative Asset, balance sheet location	Other assets		Other assets
Interest rate swaps, amount reclassified from AOCI	$ (1,561)	$ (1,667)	$ (5,179)	$ (3,724)
Interest rate swaps, future amount to be reclassified from AOCI			(4,300)
Interest rate swaps, collateral held	(7,300)		(7,300)		(14,000)
FHLB advances [Member]
FHLB Advances, Amount	$ 2,290,000		2,290,000		2,380,000
Federal Reserve Bank Advances [Member]
BTFP borrowings					$ 500,000
Repayments on borrowings			$ 500,000