Securities (Schedule Of Estimated Fair Value And Gross Unrealized Losses Of Securities In Continuous Unrealized Loss Position) (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Sep. 30, 2021
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value	$ 1,402,095	$ 1,398,300
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	21,635	12,488
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value	45,877	10,612
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses	850	65
MBS [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value	891,031	881,975
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	12,727	8,843
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Estimated Fair Value	45,877	10,612
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses	850	65
GSE Debentures [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Estimated Fair Value	511,064	516,325
Available-for-sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Unrealized Losses	8,908	3,645
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
Municipal Bonds [Member]
Schedule of Investments [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	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Equal to or Greater Than 12 Months, Unrealized Losses	$ 0	$ 0