Loans Receivable and Allowance for Loan Losses: Impaired Financing Receivables (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	$ 3,830	$ 9,942	$ 11,059
Impaired Financing Receivable, with Related Allowance, Recorded Investment	3,162	6,295	13,372
Impaired Financing Receivable, Recorded Investment	6,992	16,237	24,431
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	4,089	11,806	13,133
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	3,221	6,295	13,372
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	7,310	18,101	26,505
Impaired Financing Receivable, Related Allowance	476	776	1,011
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	5,963	10,476	12,983
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	5,260	8,103	14,458
Impaired Financing Receivable, Average Recorded Investment	11,223	18,579	27,441
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	271	475	574
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	296	478	585
Impaired Financing Receivable, Interest Income Recognized	567	953	1,159
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	218	380	460
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized	237	378	443
Impaired Financing Receivable, Cash Basis Interest Income Recognized	455	758	903
Mortgage loans, one-to-four family
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,443	914	1,321
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	1,350	2,970
Impaired Financing Receivable, Recorded Investment	1,443	2,264	4,291
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	1,589	1,060	1,546
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	1,350	2,970
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	1,589	2,410	4,516
Impaired Financing Receivable, Related Allowance	0	70	307
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	1,108	1,349	1,919
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	721	1,921	3,833
Impaired Financing Receivable, Average Recorded Investment	1,829	3,270	5,752
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	68	38	25
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	50	118	149
Impaired Financing Receivable, Interest Income Recognized	118	156	174
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	62	38	25
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized	38	89	112
Impaired Financing Receivable, Cash Basis Interest Income Recognized	100	127	137
Mortgage loans, multi-family
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment		0	760
Impaired Financing Receivable, with Related Allowance, Recorded Investment		0	3,277
Impaired Financing Receivable, Recorded Investment		0	4,037
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)		0	791
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)		0	3,277
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)		0	4,068
Impaired Financing Receivable, Related Allowance		0	16
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment		152	570
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment		655	3,291
Impaired Financing Receivable, Average Recorded Investment		807	3,861
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized		0	3
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized		0	184
Impaired Financing Receivable, Interest Income Recognized		0	187
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized		0	3
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized		0	137
Impaired Financing Receivable, Cash Basis Interest Income Recognized		0	140
Mortgage loans, commercial
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	1,967	7,566	7,199
Impaired Financing Receivable, with Related Allowance, Recorded Investment	1,906	3,743	5,653
Impaired Financing Receivable, Recorded Investment	3,873	11,309	12,852
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	1,967	8,685	8,259
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	1,906	3,743	5,653
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	3,873	12,428	13,912
Impaired Financing Receivable, Related Allowance	26	413	265
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	3,901	7,784	9,078
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	3,326	4,181	3,475
Impaired Financing Receivable, Average Recorded Investment	7,227	11,965	12,553
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	188	421	521
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	182	275	202
Impaired Financing Receivable, Interest Income Recognized	370	696	723
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	143	330	412
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized	144	215	152
Impaired Financing Receivable, Cash Basis Interest Income Recognized	287	545	564
Mortgage loans, construction - custom and owner/builder
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	367	0
Impaired Financing Receivable, with Related Allowance, Recorded Investment			0
Impaired Financing Receivable, Recorded Investment	0	367	0
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	367	0
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)			0
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	367	0
Impaired Financing Receivable, Related Allowance	0	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	147	73	118
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment			17
Impaired Financing Receivable, Average Recorded Investment	147	73	135
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	7	0	0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized			0
Impaired Financing Receivable, Interest Income Recognized	7	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	7	0	0
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized			0
Impaired Financing Receivable, Cash Basis Interest Income Recognized	7	0	0
Mortgage loans, land
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	297	693	1,614
Impaired Financing Receivable, with Related Allowance, Recorded Investment	822	575	691
Impaired Financing Receivable, Recorded Investment	1,119	1,268	2,305
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	410	1,101	2,150
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	881	575	691
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	1,291	1,676	2,841
Impaired Financing Receivable, Related Allowance	125	53	37
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	512	839	1,028
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	666	604	3,298
Impaired Financing Receivable, Average Recorded Investment	1,178	1,443	4,326
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	8	16	25
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	35	39	32
Impaired Financing Receivable, Interest Income Recognized	43	55	57
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	6	12	20
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized	29	32	27
Impaired Financing Receivable, Cash Basis Interest Income Recognized	35	44	47
Consumer loans, home equity and second mortgage
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	123	402	165
Impaired Financing Receivable, with Related Allowance, Recorded Investment	434	597	745
Impaired Financing Receivable, Recorded Investment	557	999	910
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	123	593	381
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	434	597	745
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	557	1,190	1,126
Impaired Financing Receivable, Related Allowance	325	227	362
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	284	264	270
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	530	709	516
Impaired Financing Receivable, Average Recorded Investment	814	973	786
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	0	0	0
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	29	44	18
Impaired Financing Receivable, Interest Income Recognized	29	44	18
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	0	0	0
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized	26	40	15
Impaired Financing Receivable, Cash Basis Interest Income Recognized	26	40	15
Consumer loans, other
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with Related Allowance, Recorded Investment	0	30	36
Impaired Financing Receivable, Recorded Investment	0	30	36
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	30	36
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	30	36
Impaired Financing Receivable, Related Allowance	0	13	24
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with Related Allowance, Average Recorded Investment	17	33	28
Impaired Financing Receivable, Average Recorded Investment	17	33	28
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with Related Allowance, Interest Income Recognized	0	2	0
Impaired Financing Receivable, Interest Income Recognized	0	2	0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with Related Allowance, Cash Basis Interest Income Recognized	0	2	0
Impaired Financing Receivable, Cash Basis Interest Income Recognized	0	2	0
Commercial business loans
Impaired Financing Receivable, Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Recorded Investment	0	0	0
Impaired Financing Receivable, Recorded Investment	0	0	0
Impaired Financing Receivable, Unpaid Principal Balance [Abstract]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	0	6
Impaired Financing Receivable, Unpaid Principal Balance (Loan Balance Plus Charge Off)	0	0	6
Impaired Financing Receivable, Related Allowance	0	0	0
Impaired Financing Receivable, Average Recorded Investment [Abstract]
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	11	15	0
Impaired Financing Receivable, Average Recorded Investment	11	15	0
Impaired Financing Receivable, Interest Income, Accrual Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Interest Income Recognized	0	0	0
Impaired Financing Receivable, Interest Income Recognized	0	0	0
Impaired Financing Receivable, Interest Income, Cash Basis Method [Abstract]
Impaired Financing Receivable, with No Related Allowance, Cash Basis Interest Income Recognized	0	0	0
Impaired Financing Receivable, Cash Basis Interest Income Recognized	$ 0	$ 0	$ 0

Loans Receivable and Allowance for Loan Losses: Impaired Financing Receivables (Details) - USD ($)
$ in Thousands

12 Months Ended

Sep. 30, 2017

Sep. 30, 2016

Sep. 30, 2015

Impaired Financing Receivable, Recorded Investment [Abstract]

Impaired Financing Receivable, with No Related Allowance, Recorded Investment

$ 3,830

$ 9,942

$ 11,059

Impaired Financing Receivable, with Related Allowance, Recorded Investment

3,162