Loans Receivable and Allowance for Credit Losses - Credit Quality Indicators (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Total Loans
Total	$ 7,751,328		$ 7,641,593
Total gross charge-offs
Total	281	$ 57
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	214,551		1,836,787
2022	1,864,222		1,697,890
2021	1,688,733		710,769
2020	686,118		694,400
2019	662,426		451,367
Prior	2,218,214		1,831,970
Revolving Loans	400,393		400,894
Revolving Loans to Term Loans	426		457
Total	7,735,083		7,624,534
Total gross charge-offs
2023	0		10
2022	5		18
2021	30		50
2020	0		143
2019	0		151
Prior	246		266
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	281		638
Real estate loans | One-to-four family
Total Loans
Total	2,862,917		2,862,342
Total gross charge-offs
Total	134	0
Real estate loans | One-to-four family | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	20,462		829,363
2022	848,150		836,996
2021	831,900		294,721
2020	289,824		177,795
2019	174,899		125,377
Prior	695,729		595,932
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,860,964		2,860,184
Total gross charge-offs
2023	0		0
2022	0		0
2021	0		50
2020	0		0
2019	0		122
Prior	134		210
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	134		382
Real estate loans | One-to-four family | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	20,462		829,363
2022	848,150		836,355
2021	831,259		294,721
2020	289,824		177,114
2019	174,220		125,057
Prior	694,583		595,097
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,858,498		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	0		0
2022	0		0
2021	0		0
2020	0		0
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
2023	0		0
2022	0		641
2021	641		0
2020	0		681
2019	679		320
Prior	1,146		835
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,466		2,477
Real estate loans | Multifamily
Total Loans
Total	1,315,143		1,239,207
Total gross charge-offs
Total	0	0
Real estate loans | Multifamily | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	91,142		315,157
2022	312,669		309,611
2021	308,390		167,955
2020	160,035		205,608
2019	204,633		38,849
Prior	238,274		202,027
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	1,315,143		1,239,207
Total gross charge-offs
2023	0		0
2022	0		0
2021	0		0
2020	0		0
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
2023	91,142		315,157
2022	312,669		309,611
2021	308,390		167,955
2020	160,035		205,608
2019	204,633		38,849
Prior	233,740		197,489
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	1,310,609		1,234,669
Real estate loans | Multifamily | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		0
2021	0		0
2020	0		0
2019	0		0
Prior	4,534		4,538
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	4,534		4,538
Real estate loans | Multifamily | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		0
2021	0		0
2020	0		0
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	2,406,590		2,426,510
Total gross charge-offs
Total	86	0
Real estate loans | Commercial real estate | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	50,010		448,313
2022	430,326		393,167
2021	392,438		173,254
2020	170,765		262,767
2019	249,107		247,366
Prior	1,101,272		888,527
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,393,918		2,413,394
Total gross charge-offs
2023	0		0
2022	0		0
2021	0		0
2020	0		0
2019	0		0
Prior	86		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	86		0
Real estate loans | Commercial real estate | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	50,010		448,313
2022	430,326		392,689
2021	391,963		170,125
2020	167,649		260,268
2019	246,612		231,868
Prior	1,037,991		852,104
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	2,324,551		2,355,367
Real estate loans | Commercial real estate | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		478
2021	475		1,843
2020	0		892
2019	888		15,498
Prior	46,046		20,939
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	47,409		39,650
Real estate loans | Commercial real estate | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		0
2021	0		1,286
2020	3,116		1,607
2019	1,607		0
Prior	17,235		15,484
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	21,958		18,377
Real estate loans | Construction
Total Loans
Total	375,474		337,593
Total gross charge-offs
Total	0	0
Real estate loans | Construction | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	24,441		159,751
2022	195,969		104,339
2021	101,388		28,058
2020	20,638		14,216
2019	1,382		870
Prior	30,616		29,319
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	374,434		336,553
Total gross charge-offs
2023	0		0
2022	0		0
2021	0		0
2020	0		0
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
2023	24,441		159,751
2022	195,969		104,339
2021	101,388		28,058
2020	20,638		14,216
2019	1,382		870
Prior	30,616		29,319
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	374,434		336,553
Real estate loans | Construction | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		0
2021	0		0
2020	0		0
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
2023	0		0
2022	0		0
2021	0		0
2020	0		0
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	517,116		497,965
Total gross charge-offs
Total	0	27
Commercial business loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	23,304		58,631
2022	54,209		33,214
2021	34,938		32,911
2020	31,868		21,842
2019	20,753		27,749
Prior	56,511		27,630
Revolving Loans	295,099		295,492
Revolving Loans to Term Loans	0		0
Total	516,682		497,469
Total gross charge-offs
2023	0		0
2022	0		0
2021	0		0
2020	0		143
2019	0		29
Prior	0		18
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	0		190
Commercial business loans | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	23,304		58,631
2022	54,209		32,880
2021	34,624		32,788
2020	31,811		20,705
2019	19,711		24,634
Prior	48,713		27,277
Revolving Loans	283,464		280,857
Revolving Loans to Term Loans	0		0
Total	495,836		477,772
Commercial business loans | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		110
2021	90		63
2020	47		1,137
2019	1,042		1,030
Prior	1,015		38
Revolving Loans	4,367		10,761
Revolving Loans to Term Loans	0		0
Total	6,561		13,139
Commercial business loans | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		224
2021	224		60
2020	10		0
2019	0		2,085
Prior	6,783		315
Revolving Loans	7,268		3,874
Revolving Loans to Term Loans	0		0
Total	14,285		6,558
Consumer loans | Home equity loans and advances
Total Loans
Total	271,766		274,551
Total gross charge-offs
Total	26	27
Consumer loans | Home equity loans and advances | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	3,751		22,903
2022	22,676		20,476
2021	19,615		13,770
2020	12,896		12,070
2019	11,581		11,126
Prior	95,703		88,439
Revolving Loans	104,972		105,061
Revolving Loans to Term Loans	426		457
Total	271,620		274,302
Total gross charge-offs
2023	0		0
2022	0		0
2021	0		0
2020	0		0
2019	0		0
Prior	26		33
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	26		33
Consumer loans | Home equity loans and advances | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	3,751		22,903
2022	22,676		20,476
2021	19,615		13,770
2020	12,896		12,070
2019	11,581		11,126
Prior	95,538		88,251
Revolving Loans	104,936		105,005
Revolving Loans to Term Loans	426		457
Total	271,419		274,058
Consumer loans | Home equity loans and advances | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		0
2021	0		0
2020	0		0
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
2023	0		0
2022	0		0
2021	0		0
2020	0		0
2019	0		0
Prior	165		188
Revolving Loans	36		56
Revolving Loans to Term Loans	0		0
Total	201		244
Consumer loans | Other consumer loans
Total Loans
Total	2,322		3,425
Total gross charge-offs
Total	35	$ 3
Consumer loans | Other consumer loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	1,441		2,669
2022	223		87
2021	64		100
2020	92		102
2019	71		30
Prior	109		96
Revolving Loans	322		341
Revolving Loans to Term Loans	0		0
Total	2,322		3,425
Total gross charge-offs
2023	0		10
2022	5		18
2021	30		0
2020	0		0
2019	0		0
Prior	0		5
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	35		33
Consumer loans | Other consumer loans | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	1,441		2,669
2022	223		87
2021	64		100
2020	92		102
2019	71		30
Prior	109		96
Revolving Loans	322		341
Revolving Loans to Term Loans	0		0
Total	2,322		3,425
Consumer loans | Other consumer loans | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Total Loans
2023	0		0
2022	0		0
2021	0		0
2020	0		0
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
2023	0		0
2022	0		0
2021	0		0
2020	0		0
2019	0		0
Prior	0		0
Revolving Loans	0		0
Revolving Loans to Term Loans	0		0
Total	$ 0		$ 0