Loans Receivable and Allowance for Credit Losses - Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Total Loans
Total	$ 7,806,180		$ 7,806,180		$ 7,641,593
Total gross charge-offs
Total	2,396	$ 302	3,231	$ 487
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	508,688		508,688		1,836,787
2022/2021	1,861,869		1,861,869		1,697,890
2021/2020	1,655,831		1,655,831		710,769
2020/2019	661,923		661,923		694,400
2019/2018	643,275		643,275		451,367
Prior	2,046,749		2,046,749		1,831,970
Revolving Loans	412,191		412,191		400,894
Revolving Loans to Term Loans	426		426		457
Total	7,790,952		7,790,952		7,624,534
Total gross charge-offs
2023/2022			0		10
2022/2021			43		18
2021/2020			273		50
2020/2019			34		143
2019/2018			2,313		151
Prior			568		266
Revolving Loans			0		0
Revolving Loans to Term Loans			0		0
Total			3,231		638
Real estate loans | One-to-four family
Total Loans
Total	2,793,852		2,793,852		2,862,342
Total gross charge-offs
Total	218	284	352	377
Real estate loans | One-to-four family | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	100,102		100,102		829,363
2022/2021	796,213		796,213		836,996
2021/2020	806,745		806,745		294,721
2020/2019	277,905		277,905		177,795
2019/2018	169,076		169,076		125,377
Prior	641,898		641,898		595,932
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	2,791,939		2,791,939		2,860,184
Total gross charge-offs
2023/2022			0		0
2022/2021			3		0
2021/2020			197		50
2020/2019			0		0
2019/2018			0		122
Prior			152		210
Revolving Loans			0		0
Revolving Loans to Term Loans			0		0
Total			352		382
Real estate loans | One-to-four family | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	100,102		100,102		829,363
2022/2021	794,991		794,991		836,355
2021/2020	806,192		806,192		294,721
2020/2019	277,750		277,750		177,114
2019/2018	168,116		168,116		125,057
Prior	640,209		640,209		595,097
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	2,787,360		2,787,360		2,857,707
Real estate loans | One-to-four family | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	0		0		0
Real estate loans | One-to-four family | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	1,222		1,222		641
2021/2020	553		553		0
2020/2019	155		155		681
2019/2018	960		960		320
Prior	1,689		1,689		835
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	4,579		4,579		2,477
Real estate loans | Multifamily
Total Loans
Total	1,417,233		1,417,233		1,239,207
Total gross charge-offs
Total	0	0	0	0
Real estate loans | Multifamily | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	107,375		107,375		315,157
2022/2021	321,281		321,281		309,611
2021/2020	361,644		361,644		167,955
2020/2019	160,831		160,831		205,608
2019/2018	204,079		204,079		38,849
Prior	262,023		262,023		202,027
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	1,417,233		1,417,233		1,239,207
Total gross charge-offs
2023/2022			0		0
2022/2021			0		0
2021/2020			0		0
2020/2019			0		0
2019/2018			0		0
Prior			0		0
Revolving Loans			0		0
Revolving Loans to Term Loans			0		0
Total			0		0
Real estate loans | Multifamily | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	107,375		107,375		315,157
2022/2021	315,525		315,525		309,611
2021/2020	361,644		361,644		167,955
2020/2019	160,831		160,831		205,608
2019/2018	204,079		204,079		38,849
Prior	257,498		257,498		197,489
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	1,406,952		1,406,952		1,234,669
Real estate loans | Multifamily | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	4,525		4,525		4,538
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	4,525		4,525		4,538
Real estate loans | Multifamily | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	5,756		5,756		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	5,756		5,756		0
Real estate loans | Commercial real estate
Total Loans
Total	2,386,237		2,386,237		2,426,510
Total gross charge-offs
Total	0	0	150	0
Real estate loans | Commercial real estate | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	167,016		167,016		448,313
2022/2021	417,317		417,317		393,167
2021/2020	369,902		369,902		173,254
2020/2019	178,064		178,064		262,767
2019/2018	241,390		241,390		247,366
Prior	1,000,799		1,000,799		888,527
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	2,374,488		2,374,488		2,413,394
Total gross charge-offs
2023/2022			0		0
2022/2021			0		0
2021/2020			0		0
2020/2019			0		0
2019/2018			64		0
Prior			86		0
Revolving Loans			0		0
Revolving Loans to Term Loans			0		0
Total			150		0
Real estate loans | Commercial real estate | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	167,016		167,016		448,313
2022/2021	417,317		417,317		392,689
2021/2020	368,522		368,522		170,125
2020/2019	174,970		174,970		260,268
2019/2018	240,513		240,513		231,868
Prior	967,119		967,119		852,104
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	2,335,457		2,335,457		2,355,367
Real estate loans | Commercial real estate | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		478
2021/2020	469		469		1,843
2020/2019	0		0		892
2019/2018	877		877		15,498
Prior	20,620		20,620		20,939
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	21,966		21,966		39,650
Real estate loans | Commercial real estate | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	911		911		1,286
2020/2019	3,094		3,094		1,607
2019/2018	0		0		0
Prior	13,060		13,060		15,484
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	17,065		17,065		18,377
Real estate loans | Construction
Total Loans
Total	391,979		391,979		337,593
Total gross charge-offs
Total	0	0	0	0
Real estate loans | Construction | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	61,208		61,208		159,751
2022/2021	252,894		252,894		104,339
2021/2020	68,281		68,281		28,058
2020/2019	4,933		4,933		14,216
2019/2018	440		440		870
Prior	3,184		3,184		29,319
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	390,940		390,940		336,553
Total gross charge-offs
2023/2022			0		0
2022/2021			0		0
2021/2020			0		0
2020/2019			0		0
2019/2018			0		0
Prior			0		0
Revolving Loans			0		0
Revolving Loans to Term Loans			0		0
Total			0		0
Real estate loans | Construction | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	61,208		61,208		159,751
2022/2021	252,894		252,894		104,339
2021/2020	68,281		68,281		28,058
2020/2019	4,933		4,933		14,216
2019/2018	440		440		870
Prior	3,184		3,184		29,319
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	390,940		390,940		336,553
Real estate loans | Construction | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	0		0		0
Real estate loans | Construction | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	0		0		0
Commercial business loans
Total Loans
Total	547,138		547,138		497,965
Total gross charge-offs
Total	2,168	0	2,618	62
Commercial business loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	56,210		56,210		58,631
2022/2021	52,721		52,721		33,214
2021/2020	30,584		30,584		32,911
2020/2019	28,495		28,495		21,842
2019/2018	17,869		17,869		27,749
Prior	50,708		50,708		27,630
Revolving Loans	310,163		310,163		295,492
Revolving Loans to Term Loans	0		0		0
Total	546,750		546,750		497,469
Total gross charge-offs
2023/2022			0		0
2022/2021			0		0
2021/2020			31		0
2020/2019			34		143
2019/2018			2,249		29
Prior			304		18
Revolving Loans			0		0
Revolving Loans to Term Loans			0		0
Total			2,618		190
Commercial business loans | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	56,079		56,079		58,631
2022/2021	52,324		52,324		32,880
2021/2020	30,412		30,412		32,788
2020/2019	28,374		28,374		20,705
2019/2018	16,834		16,834		24,634
Prior	42,735		42,735		27,277
Revolving Loans	294,125		294,125		280,857
Revolving Loans to Term Loans	0		0		0
Total	520,883		520,883		477,772
Commercial business loans | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	131		131		0
2022/2021	321		321		110
2021/2020	49		49		63
2020/2019	114		114		1,137
2019/2018	0		0		1,030
Prior	2,284		2,284		38
Revolving Loans	6,904		6,904		10,761
Revolving Loans to Term Loans	0		0		0
Total	9,803		9,803		13,139
Commercial business loans | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	76		76		224
2021/2020	123		123		60
2020/2019	7		7		0
2019/2018	1,035		1,035		2,085
Prior	5,689		5,689		315
Revolving Loans	9,134		9,134		3,874
Revolving Loans to Term Loans	0		0		0
Total	16,064		16,064		6,558
Consumer loans | Home equity loans and advances
Total Loans
Total	267,155		267,155		274,551
Total gross charge-offs
Total	0	6	25	33
Consumer loans | Home equity loans and advances | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	14,856		14,856		22,903
2022/2021	21,272		21,272		20,476
2021/2020	18,628		18,628		13,770
2020/2019	11,684		11,684		12,070
2019/2018	10,387		10,387		11,126
Prior	88,047		88,047		88,439
Revolving Loans	101,716		101,716		105,061
Revolving Loans to Term Loans	426		426		457
Total	267,016		267,016		274,302
Total gross charge-offs
2023/2022			0		0
2022/2021			0		0
2021/2020			0		0
2020/2019			0		0
2019/2018			0		0
Prior			25		33
Revolving Loans			0		0
Revolving Loans to Term Loans			0		0
Total			25		33
Consumer loans | Home equity loans and advances | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	14,856		14,856		22,903
2022/2021	21,272		21,272		20,476
2021/2020	18,628		18,628		13,770
2020/2019	11,684		11,684		12,070
2019/2018	10,387		10,387		11,126
Prior	87,826		87,826		88,251
Revolving Loans	101,716		101,716		105,005
Revolving Loans to Term Loans	426		426		457
Total	266,795		266,795		274,058
Consumer loans | Home equity loans and advances | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	0		0		0
Consumer loans | Home equity loans and advances | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	221		221		188
Revolving Loans	0		0		56
Revolving Loans to Term Loans	0		0		0
Total	221		221		244
Consumer loans | Other consumer loans
Total Loans
Total	2,586		2,586		3,425
Total gross charge-offs
Total	10	$ 12	86	$ 15
Consumer loans | Other consumer loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	1,921		1,921		2,669
2022/2021	171		171		87
2021/2020	47		47		100
2020/2019	11		11		102
2019/2018	34		34		30
Prior	90		90		96
Revolving Loans	312		312		341
Revolving Loans to Term Loans	0		0		0
Total	2,586		2,586		3,425
Total gross charge-offs
2023/2022			0		10
2022/2021			40		18
2021/2020			45		0
2020/2019			0		0
2019/2018			0		0
Prior			1		5
Revolving Loans			0		0
Revolving Loans to Term Loans			0		0
Total			86		33
Consumer loans | Other consumer loans | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	1,921		1,921		2,669
2022/2021	171		171		87
2021/2020	47		47		100
2020/2019	11		11		102
2019/2018	34		34		30
Prior	90		90		96
Revolving Loans	312		312		341
Revolving Loans to Term Loans	0		0		0
Total	2,586		2,586		3,425
Consumer loans | Other consumer loans | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	0		0		0
Consumer loans | Other consumer loans | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023/2022	0		0		0
2022/2021	0		0		0
2021/2020	0		0		0
2020/2019	0		0		0
2019/2018	0		0		0
Prior	0		0		0
Revolving Loans	0		0		0
Revolving Loans to Term Loans	0		0		0
Total	$ 0		$ 0		$ 0