Loans Receivable - Loans Based on Credit Quality Indicators (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Sep. 30, 2022
Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023		$ 0
2022		1,594
2021		0
2020		0
2019		0
Prior to 2019		0
Revolving Loans		0
Revolving to Term Loans		0
Total Loans		1,594
Commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	$ 372,249	2,351,822
2022	2,509,270	2,646,527
2021	2,593,210	1,316,898
2020	1,297,514	574,962
2019	571,392	422,204
Prior to 2019	1,456,736	1,120,742
Revolving Loans	1,556,712	1,295,091
Revolving to Term Loans	1,911	255
Total Loans	10,358,994	9,728,501
Commercial loans | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	372,249	2,343,088
2022	2,485,829	2,630,037
2021	2,573,937	1,299,292
2020	1,261,433	539,354
2019	534,822	409,574
Prior to 2019	1,407,932	1,082,730
Revolving Loans	1,467,037	1,204,597
Revolving to Term Loans	1,911	255
Total Loans	10,105,150	9,508,927
Commercial loans | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	2,503
2022	0	1,594
2021	2,601	0
2020	0	0
2019	1,382	0
Prior to 2019	0	0
Revolving Loans	2,850	29,153
Revolving to Term Loans	0	0
Total Loans	6,833	33,250
Commercial loans | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	6,231
2022	23,441	14,896
2021	16,672	17,606
2020	36,081	35,608
2019	35,188	12,630
Prior to 2019	48,804	38,012
Revolving Loans	86,825	61,341
Revolving to Term Loans	0	0
Total Loans	247,011	186,324
Commercial loans | Multi-family
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	94,649	661,095
2022	670,726	778,936
2021	763,102	502,646
2020	490,648	168,568
2019	167,495	163,704
Prior to 2019	472,778	317,428
Revolving Loans	36,361	34,102
Revolving to Term Loans	0	0
Total Loans	2,695,759	2,626,479
Commercial loans | Multi-family | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	94,649	657,144
2022	666,795	778,936
2021	763,102	500,917
2020	486,468	168,568
2019	167,495	157,144
Prior to 2019	464,692	315,858
Revolving Loans	36,361	34,102
Revolving to Term Loans	0	0
Total Loans	2,679,562	2,612,669
Commercial loans | Multi-family | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	3,951
2022	3,931	0
2021	0	1,729
2020	4,180	0
2019	0	6,560
Prior to 2019	8,086	1,570
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	16,197	13,810
Commercial loans | Commercial real estate
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	130,440	820,749
2022	812,040	680,915
2021	723,882	498,900
2020	494,025	331,612
2019	328,075	223,028
Prior to 2019	720,901	551,931
Revolving Loans	3,945	3,977
Revolving to Term Loans	0	0
Total Loans	3,213,308	3,111,112
Commercial loans | Commercial real estate | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	130,440	820,490
2022	806,478	679,321
2021	722,298	492,826
2020	467,416	301,033
2019	296,176	218,171
Prior to 2019	705,610	541,008
Revolving Loans	1,375	1,391
Revolving to Term Loans	0	0
Total Loans	3,129,793	3,054,240
Commercial loans | Commercial real estate | Special mention
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0
2022	0
2021	0
2020	0
2019	1,382
Prior to 2019	0
Revolving Loans	0
Revolving to Term Loans	0
Total Loans	1,382
Commercial loans | Commercial real estate | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	259
2022	5,562	0
2021	1,584	6,074
2020	26,609	30,579
2019	30,517	4,857
Prior to 2019	15,291	10,923
Revolving Loans	2,570	2,586
Revolving to Term Loans	0	0
Total Loans	82,133	55,278
Commercial loans | Commercial & industrial
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	124,523	259,192
2022	280,121	448,269
2021	360,596	155,602
2020	140,225	44,131
2019	39,256	26,922
Prior to 2019	236,750	223,428
Revolving Loans	1,437,884	1,185,604
Revolving to Term Loans	1,911	255
Total Loans	2,621,266	2,343,403
Commercial loans | Commercial & industrial | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	124,523	254,668
2022	272,160	435,630
2021	345,166	145,799
2020	134,933	39,102
2019	34,585	25,709
Prior to 2019	211,323	197,909
Revolving Loans	1,350,779	1,097,696
Revolving to Term Loans	1,911	255
Total Loans	2,475,380	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	2,601	0
2020	0	0
2019	0	0
Prior to 2019	0	0
Revolving Loans	2,850	29,153
Revolving to Term Loans	0	0
Total Loans	5,451	31,656
Commercial loans | Commercial & industrial | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	2,021
2022	7,961	12,639
2021	12,829	9,803
2020	5,292	5,029
2019	4,671	1,213
Prior to 2019	25,427	25,519
Revolving Loans	84,255	58,755
Revolving to Term Loans	0	0
Total Loans	140,435	114,979
Commercial loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	17,955	510,764
2022	657,795	673,868
2021	696,773	142,816
2020	155,086	27,260
2019	33,585	375
Prior to 2019	375	0
Revolving Loans	75,930	68,808
Revolving to Term Loans	0	0
Total Loans	1,637,499	1,423,891
Commercial loans | Construction | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	17,955	510,764
2022	651,808	671,611
2021	694,514	142,816
2020	155,086	27,260
2019	33,585	375
Prior to 2019	375	0
Revolving Loans	75,930	68,808
Revolving to Term Loans	0	0
Total Loans	1,629,253	1,421,634
Commercial loans | Construction | Substandard
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	5,987	2,257
2021	2,259	0
2020	0	0
2019	0	0
Prior to 2019	0	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	8,246	2,257
Commercial loans | Land - acquisition & development
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	4,682	100,022
2022	88,588	64,539
2021	48,857	16,934
2020	17,530	3,391
2019	2,981	8,175
Prior to 2019	25,932	27,955
Revolving Loans	2,592	2,600
Revolving to Term Loans	0	0
Total Loans	191,162	223,616
Commercial loans | Land - acquisition & development | Pass
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	4,682	100,022
2022	88,588	64,539
2021	48,857	16,934
2020	17,530	3,391
2019	2,981	8,175
Prior to 2019	25,932	27,955
Revolving Loans	2,592	2,600
Revolving to Term Loans	0	0
Total Loans	191,162	223,616
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	224,142	1,420,965
2022	1,520,989	1,873,721
2021	1,867,755	806,033
2020	796,591	328,430
2019	320,649	303,923
Prior to 2019	1,847,441	1,598,038
Revolving Loans	233,299	225,772
Revolving to Term Loans	525	989
Total Loans	6,811,391	6,557,871
Consumer loans | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	224,142	1,420,964
2022	1,520,987	1,873,286
2021	1,865,683	805,494
2020	796,591	327,315
2019	319,469	303,923
Prior to 2019	1,828,221	1,581,180
Revolving Loans	231,293	225,461
Revolving to Term Loans	525	989
Total Loans	6,786,911	6,538,612
Consumer loans | 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	1,637	400
2020	0	606
2019	63	0
Prior to 2019	4,307	2,040
Revolving Loans	1,878	67
Revolving to Term Loans	0	0
Total Loans	7,885	3,113
Consumer loans | 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	0	139
2020	0	0
2019	1	0
Prior to 2019	2,211	1,362
Revolving Loans	0	17
Revolving to Term Loans	0	0
Total Loans	2,212	1,518
Consumer loans | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	1
2022	2	435
2021	435	0
2020	0	509
2019	1,116	0
Prior to 2019	12,702	13,456
Revolving Loans	128	227
Revolving to Term Loans	0	0
Total Loans	14,383	14,628
Consumer loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	235,030
2022	320,079	150,869
2021	82,784	9,811
2020	4,864	1,155
2019	358	478
Prior to 2019	478	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	408,563	397,343
Consumer loans | Construction | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	235,030
2022	320,079	150,434
2021	82,349	9,811
2020	4,864	1,155
2019	358	478
Prior to 2019	478	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	408,128	396,908
Consumer loans | Construction | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	435
2021	435	0
2020	0	0
2019	0	0
Prior to 2019	0	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	435	435
Consumer loans | Single-family residential
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	219,679	1,131,152
2022	1,148,027	1,652,242
2021	1,719,327	772,169
2020	768,368	321,627
2019	314,866	276,093
Prior to 2019	1,797,411	1,573,696
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	5,967,678	5,726,979
Consumer loans | Single-family residential | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	219,679	1,131,152
2022	1,148,027	1,652,242
2021	1,717,690	771,769
2020	768,368	320,546
2019	313,719	276,093
Prior to 2019	1,778,899	1,557,194
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	5,946,382	5,708,996
Consumer loans | Single-family residential | 30 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	0
2022	0	0
2021	1,637	400
2020	0	604
2019	63	0
Prior to 2019	3,961	1,792
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	5,661	2,796
Consumer loans | Single-family residential | 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	2,038	1,316
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	2,038	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	0	0
2020	0	477
2019	1,084	0
Prior to 2019	12,513	13,394
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	13,597	13,871
Consumer loans | Land - consumer lot loans
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	4,355	53,396
2022	50,736	60,454
2021	55,658	16,015
2020	15,336	5,399
2019	5,189	3,433
Prior to 2019	15,804	13,248
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	147,078	151,945
Consumer loans | Land - consumer lot loans | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	4,355	53,396
2022	50,736	60,454
2021	55,658	15,876
2020	15,336	5,399
2019	5,189	3,433
Prior to 2019	15,695	13,188
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	146,969	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	0	0
2019	0	0
Prior to 2019	49	0
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	49	139
Consumer loans | Land - consumer lot loans | 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	60	60
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	60	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	5,106	4,473
Revolving Loans	209,273	200,571
Revolving to Term Loans	525	989
Total Loans	214,904	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	4,846	4,349
Revolving Loans	207,284	200,267
Revolving to Term Loans	525	989
Total Loans	212,655	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	260	95
Revolving Loans	1,861	60
Revolving to Term Loans	0	0
Total Loans	2,121	155
Consumer loans | HELOC | 60 days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023		0
2022		0
2021		0
2020		0
2019		0
Prior to 2019		29
Revolving Loans		17
Revolving to Term Loans		0
Total Loans		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	0	0
Revolving Loans	128	227
Revolving to Term Loans	0	0
Total Loans	128	227
Consumer loans | Consumer
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	108	1,387
2022	2,147	10,156
2021	9,986	8,038
2020	8,023	249
2019	236	23,919
Prior to 2019	28,642	6,621
Revolving Loans	24,026	25,201
Revolving to Term Loans	0	0
Total Loans	73,168	75,571
Consumer loans | Consumer | Current
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	108	1,386
2022	2,145	10,156
2021	9,986	8,038
2020	8,023	215
2019	203	23,919
Prior to 2019	28,303	6,449
Revolving Loans	24,009	25,194
Revolving to Term Loans	0	0
Total Loans	72,777	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	37	153
Revolving Loans	17	7
Revolving to Term Loans	0	0
Total Loans	54	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	1	0
Prior to 2019	173	17
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	174	17
Consumer loans | Consumer | 90+ days past due
Financing Receivable, Credit Quality Indicator [Line Items]
YTD 2023	0	1
2022	2	0
2021	0	0
2020	0	32
2019	32	0
Prior to 2019	129	2
Revolving Loans	0	0
Revolving to Term Loans	0	0
Total Loans	$ 163	$ 35