Securities (Tables)

3 Months Ended

Dec. 31, 2021

Marketable Securities [Abstract]

Amortized Cost, Estimated Fair Value, And Gross Unrealized Gains And Losses Of AFS Securities

The following tables reflect the amortized cost, estimated fair value, and gross unrealized gains and losses of AFS securities at the dates presented. The majority of the MBS and investment securities portfolios are composed of securities issued by United States Government-Sponsored Enterprises ("GSEs").

	December 31, 2021
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(Dollars in thousands)
MBS	$	1,375,711	$	14,105	$	13,577	$	1,376,239
GSE debentures	519,972		—		8,908		511,064
Municipal bonds	3,344		6		—		3,350
	$	1,899,027	$	14,111	$	22,485	$	1,890,653

	September 30, 2021
			Gross		Gross		Estimated
	Amortized		Unrealized		Unrealized		Fair
	Cost		Gains		Losses		Value
	(Dollars in thousands)
MBS	$	1,484,211	$	18,690	$	8,908	$	1,493,993
GSE debentures	519,971		—		3,645		516,326
Municipal bonds	4,274		15		—		4,289
	$	2,008,456	$	18,705	$	12,553	$	2,014,608

Schedule Of Estimated Fair Value And Gross Unrealized Losses Of Securities In Continuous Unrealized Loss Position

The following tables summarize the estimated fair value and gross unrealized losses of those AFS securities on which an unrealized loss at the dates presented was reported and the continuous unrealized loss position for less than 12 months and equal to or greater than 12 months as of the dates presented.

	December 31, 2021
	Less Than 12 Months				Equal to or Greater Than 12 Months
	Estimated		Unrealized		Estimated		Unrealized
	Fair Value		Losses		Fair Value		Losses
	(Dollars in thousands)
MBS	$	891,031	$	12,727	$	45,877	$	850
GSE debentures	511,064		8,908		—		—
Municipal bonds	—		—		—		—
	$	1,402,095	$	21,635	$	45,877	$	850

	September 30, 2021
	Less Than 12 Months				Equal to or Greater Than 12 Months
	Estimated		Unrealized		Estimated		Unrealized
	Fair Value		Losses		Fair Value		Losses
	(Dollars in thousands)
MBS	$	881,975	$	8,843	$	10,612	$	65
GSE debentures	516,325		3,645		—		—
Municipal bonds	—		—		—		—
	$	1,398,300	$	12,488	$	10,612	$	65

Schedule Of Contractual Maturities

The amortized cost and estimated fair value of AFS debt securities as of December 31, 2021, by contractual maturity, are shown below.  Actual principal repayments may differ from contractual maturities due to prepayment or early call privileges by the issuer. In the case of MBS, borrowers on the underlying loans generally have the right to prepay their loans without penalty. For this reason, MBS are not included in the maturity categories.

	Amortized		Estimated
	Cost		Fair Value
	(Dollars in thousands)
One year or less	$	3,344	$	3,350
One year through five years	519,972		511,064
	523,316		514,414
MBS	1,375,711		1,376,239
	$	1,899,027	$	1,890,653

Schedule Of Taxable And Non-taxable Components Of Interest Income

The following table presents the taxable and non-taxable components of interest income on investment securities for the periods presented.

	For the Three Months Ended
	December 31,
	2021		2020
	(Dollars in thousands)
Taxable	$	790	$	645
Non-taxable	18		38
	$	808	$	683

Schedule Of Carrying Value Of Securities Pledged As Collateral

The following table summarizes the carrying value of securities pledged as collateral for the obligations indicated below as of the dates presented.

	December 31, 2021		September 30, 2021
	(Dollars in thousands)
Public unit deposits	$	234,884	$	264,885
Federal Reserve Bank of Kansas City ("FRB of Kansas City")	59,249		64,707
Commercial deposits	44,251		66,256
	$	338,384	$	395,848