Loans Receivable - Loans Based on Credit Quality Indicators (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Sep. 30, 2022
Commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	$ 505,641	$ 2,351,822
2022	2,600,950	2,646,527
2021	2,587,764	1,316,898
2020	1,294,380	574,962
2019	546,624	422,204
Prior to 2019	1,407,969	1,120,742
Revolving Loans	1,511,866	1,295,091
Revolving to Term Loans	23,893	255
Total Loans	10,479,087	9,728,501
Commercial loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	500,938	2,343,088
2022	2,454,080	2,630,037
2021	2,556,321	1,299,292
2020	1,260,186	539,354
2019	510,352	409,574
Prior to 2019	1,353,223	1,082,730
Revolving Loans	1,415,358	1,204,597
Revolving to Term Loans	23,893	255
Total Loans	10,074,351	9,508,927
Commercial loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	4,131	2,503
2022	109,113	1,594
2021	13,542	0
2020	0	0
2019	0	0
Prior to 2019	1,558	0
Revolving Loans	0	29,153
Revolving to Term Loans	0	0
Total Loans	128,344	33,250
Commercial loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	572	6,231
2022	37,757	14,896
2021	14,942	17,606
2020	34,194	35,608
2019	36,272	12,630
Prior to 2019	53,188	38,012
Revolving Loans	92,530	61,341
Revolving to Term Loans	0	0
Total Loans	269,455	186,324
Commercial loans | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0
2022	0
2021	2,959
2020	0
2019	0
Prior to 2019	0
Revolving Loans	3,978
Revolving to Term Loans	0
Total Loans	6,937
Commercial loans | Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	119,024	661,095
2022	729,970	778,936
2021	783,279	502,646
2020	587,566	168,568
2019	152,445	163,704
Prior to 2019	449,112	317,428
Revolving Loans	38,598	34,102
Revolving to Term Loans	0	0
Total Loans	2,859,994	2,626,479
Commercial loans | Multi-family | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	119,024	657,144
2022	630,346	778,936
2021	780,948	500,917
2020	583,407	168,568
2019	152,445	157,144
Prior to 2019	441,066	315,858
Revolving Loans	38,598	34,102
Revolving to Term Loans	0	0
Total Loans	2,745,834	2,612,669
Commercial loans | Multi-family | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0
2022	94,503
2021	0
2020	0
2019	0
Prior to 2019	0
Revolving Loans	0
Revolving to Term Loans	0
Total Loans	94,503
Commercial loans | Multi-family | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	3,951
2022	5,121	0
2021	2,331	1,729
2020	4,159	0
2019	0	6,560
Prior to 2019	8,046	1,570
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	19,657	13,810
Commercial loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	166,337	820,749
2022	843,601	680,915
2021	736,463	498,900
2020	490,728	331,612
2019	316,911	223,028
Prior to 2019	700,460	551,931
Revolving Loans	3,804	3,977
Revolving to Term Loans	0	0
Total Loans	3,258,304	3,111,112
Commercial loans | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	165,837	820,490
2022	838,106	679,321
2021	732,623	492,826
2020	465,913	301,033
2019	285,084	218,171
Prior to 2019	680,459	541,008
Revolving Loans	1,350	1,391
Revolving to Term Loans	0	0
Total Loans	3,169,372	3,054,240
Commercial loans | Commercial real estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	500	0
2022	0	1,594
2021	0	0
2020	0	0
2019	0	0
Prior to 2019	0	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	500	1,594
Commercial loans | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	259
2022	5,495	0
2021	3,840	6,074
2020	24,815	30,579
2019	31,827	4,857
Prior to 2019	20,001	10,923
Revolving Loans	2,454	2,586
Revolving to Term Loans	0	0
Total Loans	88,432	55,278
Commercial loans | Commercial & industrial
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	134,976	259,192
2022	276,681	448,269
2021	351,538	155,602
2020	131,726	44,131
2019	36,203	26,922
Prior to 2019	234,949	223,428
Revolving Loans	1,395,230	1,185,604
Revolving to Term Loans	23,893	255
Total Loans	2,585,196	2,343,403
Commercial loans | Commercial & industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	134,404	254,668
2022	249,540	435,630
2021	339,808	145,799
2020	126,506	39,102
2019	31,758	25,709
Prior to 2019	208,250	197,909
Revolving Loans	1,301,176	1,097,696
Revolving to Term Loans	23,893	255
Total Loans	2,415,335	2,196,768
Commercial loans | Commercial & industrial | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	2,503
2022	0	0
2021	0	0
2020	0	0
2019	0	0
Prior to 2019	1,558	0
Revolving Loans	0	29,153
Revolving to Term Loans	0	0
Total Loans	1,558	31,656
Commercial loans | Commercial & industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	572	2,021
2022	27,141	12,639
2021	8,771	9,803
2020	5,220	5,029
2019	4,445	1,213
Prior to 2019	25,141	25,519
Revolving Loans	90,076	58,755
Revolving to Term Loans	0	0
Total Loans	161,366	114,979
Commercial loans | Commercial & industrial | Doubtful
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0
2022	0
2021	2,959
2020	0
2019	0
Prior to 2019	0
Revolving Loans	3,978
Revolving to Term Loans	0
Total Loans	6,937
Commercial loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	70,497	510,764
2022	680,480	673,868
2021	670,935	142,816
2020	74,905	27,260
2019	39,687	375
Prior to 2019	375	0
Revolving Loans	71,634	68,808
Revolving to Term Loans	0	0
Total Loans	1,608,513	1,423,891
Commercial loans | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	66,866	510,764
2022	666,139	671,611
2021	657,393	142,816
2020	74,905	27,260
2019	39,687	375
Prior to 2019	375	0
Revolving Loans	71,634	68,808
Revolving to Term Loans	0	0
Total Loans	1,576,999	1,421,634
Commercial loans | Construction | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	3,631	0
2022	14,341	2,257
2021	13,542	0
2020	0	0
2019	0	0
Prior to 2019	0	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	31,514	2,257
Commercial loans | Land - acquisition & development
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	14,807	100,022
2022	70,218	64,539
2021	45,549	16,934
2020	9,455	3,391
2019	1,378	8,175
Prior to 2019	23,073	27,955
Revolving Loans	2,600	2,600
Revolving to Term Loans	0	0
Total Loans	167,080	223,616
Commercial loans | Land - acquisition & development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	14,807	100,022
2022	69,949	64,539
2021	45,549	16,934
2020	9,455	3,391
2019	1,378	8,175
Prior to 2019	23,073	27,955
Revolving Loans	2,600	2,600
Revolving to Term Loans	0	0
Total Loans	166,811	223,616
Commercial loans | Land - acquisition & development | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0
2022	269
2021	0
2020	0
2019	0
Prior to 2019	0
Revolving Loans	0
Revolving to Term Loans	0
Total Loans	269
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	306,461	1,420,965
2022	1,676,582	1,873,721
2021	1,842,717	806,033
2020	783,804	328,430
2019	315,219	303,923
Prior to 2019	1,803,771	1,598,038
Revolving Loans	240,860	225,772
Revolving to Term Loans	825	989
Total Loans	6,970,239	6,557,871
Consumer loans | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	306,460	1,420,964
2022	1,675,493	1,873,286
2021	1,841,869	805,494
2020	782,980	327,315
2019	314,361	303,923
Prior to 2019	1,787,467	1,581,180
Revolving Loans	239,797	225,461
Revolving to Term Loans	825	989
Total Loans	6,949,252	6,538,612
Consumer loans | 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	891	0
2021	0	400
2020	824	606
2019	76	0
Prior to 2019	4,445	2,040
Revolving Loans	505	67
Revolving to Term Loans	0	0
Total Loans	6,741	3,113
Consumer loans | 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	198	0
2021	174	139
2020	0	0
2019	0	0
Prior to 2019	211	1,362
Revolving Loans	474	17
Revolving to Term Loans	0	0
Total Loans	1,057	1,518
Consumer loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	1	1
2022	0	435
2021	674	0
2020	0	509
2019	782	0
Prior to 2019	11,648	13,456
Revolving Loans	84	227
Revolving to Term Loans	0	0
Total Loans	13,189	14,628
Consumer loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	23,021	235,030
2022	341,536	150,869
2021	34,918	9,811
2020	3,472	1,155
2019	358	478
Prior to 2019	478	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	403,783	397,343
Consumer loans | Construction | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	23,021	235,030
2022	341,449	150,434
2021	34,918	9,811
2020	3,472	1,155
2019	358	478
Prior to 2019	478	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	403,696	396,908
Consumer loans | Construction | 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0
2022	87
2021	0
2020	0
2019	0
Prior to 2019	0
Revolving Loans	0
Revolving to Term Loans	0
Total Loans	87
Consumer loans | Construction | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023		0
2022		435
2021		0
2020		0
2019		0
Prior to 2019		0
Revolving Loans		0
Revolving to Term Loans		0
Total Loans		435
Consumer loans | Single-family residential
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	272,177	1,131,152
2022	1,286,526	1,652,242
2021	1,749,711	772,169
2020	758,765	321,627
2019	310,309	276,093
Prior to 2019	1,756,533	1,573,696
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	6,134,021	5,726,979
Consumer loans | Single-family residential | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	272,177	1,131,152
2022	1,285,524	1,652,242
2021	1,748,863	771,769
2020	758,020	320,546
2019	309,481	276,093
Prior to 2019	1,740,718	1,557,194
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	6,114,783	5,708,996
Consumer loans | Single-family residential | 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	804	0
2021	0	400
2020	745	604
2019	76	0
Prior to 2019	4,269	1,792
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	5,894	2,796
Consumer loans | Single-family residential | 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	198	0
2021	174	0
2020	0	0
2019	0	0
Prior to 2019	60	1,316
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	432	1,316
Consumer loans | Single-family residential | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	674	0
2020	0	477
2019	752	0
Prior to 2019	11,486	13,394
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	12,912	13,871
Consumer loans | Land - consumer lot loans
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	10,606	53,396
2022	48,382	60,454
2021	48,199	16,015
2020	13,555	5,399
2019	4,506	3,433
Prior to 2019	14,892	13,248
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	140,140	151,945
Consumer loans | Land - consumer lot loans | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	10,606	53,396
2022	48,382	60,454
2021	48,199	15,876
2020	13,476	5,399
2019	4,506	3,433
Prior to 2019	14,892	13,188
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	140,061	151,746
Consumer loans | Land - consumer lot loans | 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	139
2020	79	0
2019	0	0
Prior to 2019	0	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	79	139
Consumer loans | Land - consumer lot loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023		0
2022		0
2021		0
2020		0
2019		0
Prior to 2019		60
Revolving Loans		0
Revolving to Term Loans		0
Total Loans		60
Consumer loans | HELOC
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	0
2020	0	0
2019	0	0
Prior to 2019	4,833	4,473
Revolving Loans	215,501	200,571
Revolving to Term Loans	825	989
Total Loans	221,159	206,033
Consumer loans | HELOC | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	0
2020	0	0
2019	0	0
Prior to 2019	4,546	4,349
Revolving Loans	214,440	200,267
Revolving to Term Loans	825	989
Total Loans	219,811	205,605
Consumer loans | HELOC | 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	0
2020	0	0
2019	0	0
Prior to 2019	96	95
Revolving Loans	504	60
Revolving to Term Loans	0	0
Total Loans	600	155
Consumer loans | HELOC | 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	0
2020	0	0
2019	0	0
Prior to 2019	151	29
Revolving Loans	473	17
Revolving to Term Loans	0	0
Total Loans	624	46
Consumer loans | HELOC | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	0
2020	0	0
2019	0	0
Prior to 2019	40	0
Revolving Loans	84	227
Revolving to Term Loans	0	0
Total Loans	124	227
Consumer loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	657	1,387
2022	138	10,156
2021	9,889	8,038
2020	8,012	249
2019	46	23,919
Prior to 2019	27,035	6,621
Revolving Loans	25,359	25,201
Revolving to Term Loans	0	0
Total Loans	71,136	75,571
Consumer loans | Consumer | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	656	1,386
2022	138	10,156
2021	9,889	8,038
2020	8,012	215
2019	16	23,919
Prior to 2019	26,833	6,449
Revolving Loans	25,357	25,194
Revolving to Term Loans	0	0
Total Loans	70,901	75,357
Consumer loans | Consumer | 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	0
2020	0	2
2019	0	0
Prior to 2019	80	153
Revolving Loans	1	7
Revolving to Term Loans	0	0
Total Loans	81	162
Consumer loans | Consumer | 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	0
2020	0	0
2019	0	0
Prior to 2019	0	17
Revolving Loans	1	0
Revolving to Term Loans	0	0
Total Loans	1	17
Consumer loans | Consumer | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	1	1
2022	0	0
2021	0	0
2020	0	32
2019	30	0
Prior to 2019	122	2
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	$ 153	$ 35