Loans Receivable and Allowance for Credit Losses - Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Total Loans
Total	$ 7,780,637		$ 7,839,754
Total gross charge-offs
Total	5,122	$ 281
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	64,908		648,608
2023/2022	657,645		1,882,747
2022/2021	1,873,899		1,639,402
2021/2020	1,617,324		649,900
2020/2019	639,609		632,951
Prior	2,520,332		1,981,490
Revolving Loans	325,637		325,009
Revolving Loans to Term Loans	66,338		64,558
Total	7,765,692		7,824,665
Total gross charge-offs
2024/2023	0		0
2023/2022	24		269
2022/2021	52		280
2021/2020	2,374		34
2020/2019	0		2,342
Prior	2,672		569
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	5,122		3,494
Real estate loans | One-to-four family
Total Loans
Total	2,780,805		2,794,726
Total gross charge-offs
Total	2	134
Real estate loans | One-to-four family | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	22,636		156,279
2023/2022	158,274		787,911
2022/2021	786,650		793,843
2021/2020	784,164		272,498
2020/2019	267,500		165,966
Prior	759,708		616,336
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,778,932		2,792,833
Total gross charge-offs
2024/2023	0		0
2023/2022	0		208
2022/2021	0		197
2021/2020	0		0
2020/2019	0		29
Prior	2		151
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2		585
Real estate loans | One-to-four family | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	22,636		156,279
2023/2022	157,523		786,735
2022/2021	785,252		793,074
2021/2020	783,100		272,215
2020/2019	267,209		165,337
Prior	757,084		614,351
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,772,804		2,787,991
Real estate loans | One-to-four family | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	0		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		0
Real estate loans | One-to-four family | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	751		1,176
2022/2021	1,398		769
2021/2020	1,064		283
2020/2019	291		629
Prior	2,624		1,985
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	6,128		4,842
Real estate loans | Multifamily
Total Loans
Total	1,429,369		1,409,187
Total gross charge-offs
Total	0	0
Real estate loans | Multifamily | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		111,612
2023/2022	117,242		317,277
2022/2021	320,866		359,983
2021/2020	365,098		157,294
2020/2019	169,203		202,923
Prior	456,960		260,098
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	1,429,369		1,409,187
Total gross charge-offs
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	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
2024/2023	0		111,612
2023/2022	117,242		317,277
2022/2021	320,866		359,983
2021/2020	365,098		157,294
2020/2019	169,203		202,923
Prior	452,444		255,578
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	1,424,853		1,404,667
Real estate loans | Multifamily | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	4,516		4,520
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	4,516		4,520
Real estate loans | Multifamily | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	0		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		0
Real estate loans | Commercial real estate
Total Loans
Total	2,330,769		2,389,766
Total gross charge-offs
Total	0	86
Real estate loans | Commercial real estate | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	13,969		191,030
2023/2022	182,962		427,801
2022/2021	437,355		372,948
2021/2020	363,193		176,504
2020/2019	166,038		237,134
Prior	1,154,661		971,660
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,318,178		2,377,077
Total gross charge-offs
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		64
Prior	0		86
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		150
Real estate loans | Commercial real estate | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	13,969		191,030
2023/2022	182,962		422,058
2022/2021	431,612		371,578
2021/2020	362,730		174,705
2020/2019	164,245		236,263
Prior	1,105,621		930,740
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,261,139		2,326,374
Real estate loans | Commercial real estate | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		465
2021/2020	463		0
2020/2019	0		871
Prior	22,285		24,405
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	22,748		25,741
Real estate loans | Commercial real estate | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		5,743
2022/2021	5,743		905
2021/2020	0		1,799
2020/2019	1,793		0
Prior	26,755		16,515
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	34,291		24,962
Real estate loans | Construction
Total Loans
Total	437,566		443,094
Total gross charge-offs
Total	0	0
Real estate loans | Construction | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	6,343		99,634
2023/2022	119,856		270,397
2022/2021	251,745		65,374
2021/2020	59,622		4,933
2020/2019	0		439
Prior	0		2,317
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	437,566		443,094
Total gross charge-offs
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	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
2024/2023	6,343		99,634
2023/2022	119,856		270,397
2022/2021	251,745		65,374
2021/2020	59,622		4,933
2020/2019	0		439
Prior	0		2,317
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	437,566		443,094
Real estate loans | Construction | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	0		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		0
Real estate loans | Construction | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	0		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		0
Commercial business loans
Total Loans
Total	538,604		533,410
Total gross charge-offs
Total	5,020	0
Commercial business loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	16,089		67,656
2023/2022	59,914		58,497
2022/2021	56,860		29,077
2021/2020	27,485		27,297
2020/2019	25,868		16,594
Prior	59,291		46,493
Revolving Loans	292,753		287,427
Revolving Loans to Term Loans	0		0
Total	538,260		533,041
Total gross charge-offs
2024/2023	0		0
2023/2022	0		0
2022/2021	0		31
2021/2020	2,352		34
2020/2019	0		2,249
Prior	2,668		304
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	5,020		2,618
Commercial business loans | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	16,089		67,529
2023/2022	59,522		58,118
2022/2021	56,408		28,989
2021/2020	27,402		27,194
2020/2019	25,746		15,499
Prior	50,048		38,954
Revolving Loans	274,391		272,698
Revolving Loans to Term Loans	0		0
Total	509,606		508,981
Commercial business loans | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		127
2023/2022	0		303
2022/2021	0		0
2021/2020	0		97
2020/2019	66		14
Prior	931		1,389
Revolving Loans	1,878		4,587
Revolving Loans to Term Loans	0		0
Total	2,875		6,517
Commercial business loans | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	392		76
2022/2021	452		88
2021/2020	83		6
2020/2019	56		1,081
Prior	7,914		6,150
Revolving Loans	16,484		10,142
Revolving Loans to Term Loans	0		0
Total	25,381		17,543
Commercial business loans | Doubtful | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0
2023/2022	0
2022/2021	0
2021/2020	0
2020/2019	0
Prior	398
Revolving Loans	0
Revolving Loans to Term Loans	0
Total	398
Consumer loans | Home equity loans and advances
Total Loans
Total	260,923		266,770
Total gross charge-offs
Total	0	26
Consumer loans | Home equity loans and advances | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	3,939		20,198
2023/2022	19,264		20,713
2022/2021	20,289		18,139
2021/2020	17,744		11,368
2020/2019	10,997		9,877
Prior	89,638		84,518
Revolving Loans	32,577		37,261
Revolving Loans to Term Loans	66,338		64,558
Total	260,786		266,632
Total gross charge-offs
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	0		26
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		26
Consumer loans | Home equity loans and advances | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	3,939		20,198
2023/2022	19,264		20,713
2022/2021	20,289		18,139
2021/2020	17,744		11,368
2020/2019	10,997		9,877
Prior	89,436		84,261
Revolving Loans	32,577		37,261
Revolving Loans to Term Loans	66,338		64,558
Total	260,584		266,375
Consumer loans | Home equity loans and advances | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	0		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		0
Consumer loans | Home equity loans and advances | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	202		257
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	202		257
Consumer loans | Other consumer loans
Total Loans
Total	2,601		2,801
Total gross charge-offs
Total	100	$ 35
Consumer loans | Other consumer loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	1,932		2,199
2023/2022	133		151
2022/2021	134		38
2021/2020	18		6
2020/2019	3		18
Prior	74		68
Revolving Loans	307		321
Revolving Loans to Term Loans	0		0
Total	2,601		2,801
Total gross charge-offs
2024/2023	0		0
2023/2022	24		61
2022/2021	52		52
2021/2020	22		0
2020/2019	0		0
Prior	2		2
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	100		115
Consumer loans | Other consumer loans | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	1,932		2,199
2023/2022	133		151
2022/2021	134		38
2021/2020	18		6
2020/2019	3		18
Prior	74		68
Revolving Loans	307		321
Revolving Loans to Term Loans	0		0
Total	2,601		2,801
Consumer loans | Other consumer loans | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	0		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		0
Consumer loans | Other consumer loans | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2024/2023	0		0
2023/2022	0		0
2022/2021	0		0
2021/2020	0		0
2020/2019	0		0
Prior	0		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	$ 0		$ 0