Loans Receivable and Allowance for Loan Losses: Past Due Status of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2021		Sep. 30, 2020
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	$ 987,066		$ 1,033,725
Loans receivable, Non-Accrual	2,854	[1]	2,905	[2]
30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	5		52
60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	180		791
Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	3,039		3,748
Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	984,027		1,029,977
Mortgage loans, one-to-four family
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	119,935		118,580
Loans receivable, Non-Accrual	407	[1]	659	[2]
Mortgage loans, one-to-four family | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, one-to-four family | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	180		68
Mortgage loans, one-to-four family | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans, one-to-four family | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	587		727
Mortgage loans, one-to-four family | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	119,348		117,853
Mortgage loans, multi-family
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	87,563		85,053
Loans receivable, Non-Accrual	0	[1]	0	[2]
Mortgage loans, multi-family | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, multi-family | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, multi-family | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans, multi-family | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, multi-family | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	87,563		85,053
Mortgage loans, commercial
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	470,650		453,574
Loans receivable, Non-Accrual	773	[1]	858	[2]
Mortgage loans, commercial | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, commercial | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		519
Mortgage loans, commercial | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans, commercial | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	773		1,377
Mortgage loans, commercial | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	469,877		452,197
Mortgage loans, construction - custom and owner/builder
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	61,003		75,332
Loans receivable, Non-Accrual	0	[1]	0	[2]
Mortgage loans, construction - custom and owner/builder | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - custom and owner/builder | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - custom and owner/builder | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans, construction - custom and owner/builder | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - custom and owner/builder | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	61,003		75,332
Mortgage loans, construction - speculative one-to-four family
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	9,657		7,108
Loans receivable, Non-Accrual	0	[1]	0	[2]
Mortgage loans, construction - speculative one-to-four family | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - speculative one-to-four family | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - speculative one-to-four family | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans, construction - speculative one-to-four family | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - speculative one-to-four family | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	9,657		7,108
Mortgage loans, construction - commercial
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	38,931		20,927
Loans receivable, Non-Accrual	0	[1]	0	[2]
Mortgage loans, construction - commercial | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - commercial | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - commercial | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans, construction - commercial | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - commercial | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	38,931		20,927
Mortgage loans, construction - multi-family
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	22,888		10,832
Loans receivable, Non-Accrual	0	[1]	0	[2]
Mortgage loans, construction - multi-family | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - multi-family | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - multi-family | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans, construction - multi-family | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, construction - multi-family | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	22,888		10,832
Mortgage loans - construction - land development
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	5,502		4,739
Loans receivable, Non-Accrual	0	[1]	0	[2]
Mortgage loans - construction - land development | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans - construction - land development | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		38
Mortgage loans - construction - land development | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans - construction - land development | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		38
Mortgage loans - construction - land development | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	5,502		4,701
Mortgage loans, land
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	19,936		25,571
Loans receivable, Non-Accrual	683	[1]	394	[2]
Mortgage loans, land | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Mortgage loans, land | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		144
Mortgage loans, land | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Mortgage loans, land | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	683		538
Mortgage loans, land | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	19,253		25,033
Consumer loans, home equity and second mortgage
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	32,988		32,077
Loans receivable, Non-Accrual	516	[1]	555	[2]
Consumer loans, home equity and second mortgage | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Consumer loans, home equity and second mortgage | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		22
Consumer loans, home equity and second mortgage | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Consumer loans, home equity and second mortgage | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	516		577
Consumer loans, home equity and second mortgage | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	32,472		31,500
Consumer loans, other
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	2,512		3,572
Loans receivable, Non-Accrual	17	[1]	9	[2]
Consumer loans, other | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		3
Consumer loans, other | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Consumer loans, other | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Consumer loans, other | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	17		12
Consumer loans, other | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	2,495		3,560
Commercial business loans
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	74,579		69,540
Loans receivable, Non-Accrual	458	[1]	430	[2]
Commercial business loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	5		49
Commercial business loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
Commercial business loans | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
Commercial business loans | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	463		479
Commercial business loans | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	74,116		69,061
SBA PPP Loans
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	40,922		126,820
Loans receivable, Non-Accrual	0		0
SBA PPP Loans | 30-59 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
SBA PPP Loans | 60-89 Days Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
SBA PPP Loans | Past Due 90 Days or More and Still Accruing
Financing Receivable, Past Due [Line Items]
Past Due 90 Days or More and Still Accruing	0		0
SBA PPP Loans | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	0		0
SBA PPP Loans | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Loans receivable, Total Past Due	$ 40,922		$ 126,820

[1] Includes non-accrual loans past due 90 days or more and other loans classified as non-accrual.

[2] Includes non-accrual loans past due 90 days or more and other loans classified as non-accrual.