Securities (Schedule Of Estimated Fair Value And Gross Unrealized Losses Of Securities In Continuous Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Sep. 30, 2022
Marketable Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value	$ 76,925	$ 342,869
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	2,577	22,950
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value	1,354,699	1,185,108
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses	177,459	182,598
MBS [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value	74,190	338,013
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	2,282	22,563
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value	877,286	715,281
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses	132,889	132,448
GSE Debentures [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value	475,759	469,827
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses	44,224	50,150
Corporate Bonds [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value	1,723	3,695
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	277	305
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value	1,654	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses	346	0
Municipal Bonds [Member]
Marketable Securities [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value	1,012	1,161
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	18	82
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses	$ 0	$ 0