Loans Receivable and Allowance for Credit Losses - Credit Quality Indicators (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 6,448,554	$ 6,335,722
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	341,402	1,702,481
2021	1,689,720	771,407
2020	734,686	789,875
2019	759,980	533,879
2018	498,946	555,250
Prior	2,066,639	1,657,885
Revolving Loans	350,069	317,728
Revolving Loans to Term Loans	457	426
Total	6,441,899	6,328,931
Real estate loans | One-to-four family
Financing Receivable, Credit Quality Indicator [Line Items]
Total	2,180,121	2,092,748
Real estate loans | One-to-four family | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	134,350	793,848
2021	820,062	298,815
2020	288,339	197,707
2019	185,657	139,635
2018	131,182	135,171
Prior	620,108	527,141
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	2,179,698	2,092,317
Real estate loans | One-to-four family | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	134,350	793,848
2021	820,062	298,815
2020	288,339	196,244
2019	185,150	138,215
2018	130,336	134,811
Prior	618,808	525,615
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	2,177,045	2,087,548
Real estate loans | One-to-four family | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	0
2019	0	0
2018	0	0
Prior	0	203
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	0	203
Real estate loans | One-to-four family | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	1,463
2019	507	1,420
2018	846	360
Prior	1,300	1,323
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	2,653	4,566
Real estate loans | Multifamily
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,077,938	1,041,108
Real estate loans | Multifamily | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	68,228	312,738
2021	306,862	181,285
2020	176,040	231,252
2019	232,509	47,024
2018	49,825	131,169
Prior	244,474	137,640
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	1,077,938	1,041,108
Real estate loans | Multifamily | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	68,228	312,738
2021	306,862	181,285
2020	176,040	231,252
2019	232,509	47,024
2018	49,825	131,169
Prior	239,916	137,640
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	1,073,380	1,041,108
Real estate loans | Multifamily | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	0
2019	0	0
2018	0	0
Prior	4,558	0
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	4,558	0
Real estate loans | Multifamily | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	0
2019	0	0
2018	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
Financing Receivable, Credit Quality Indicator [Line Items]
Total	2,189,103	2,175,662
Real estate loans | Commercial real estate | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	94,039	381,222
2021	375,274	161,522
2020	160,133	279,884
2019	274,270	259,300
2018	260,784	225,913
Prior	1,019,204	862,395
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	2,183,704	2,170,236
Real estate loans | Commercial real estate | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	94,039	381,222
2021	375,274	161,136
2020	158,456	278,581
2019	273,193	241,669
2018	243,264	222,752
Prior	963,793	803,945
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	2,108,019	2,089,305
Real estate loans | Commercial real estate | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	1,303
2019	1,077	16,070
2018	15,959	1,885
Prior	30,767	34,788
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	47,803	54,046
Real estate loans | Commercial real estate | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	386
2020	1,677	0
2019	0	1,561
2018	1,561	1,276
Prior	24,644	23,662
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	27,882	26,885
Real estate loans | Construction
Financing Receivable, Credit Quality Indicator [Line Items]
Total	261,674	295,047
Real estate loans | Construction | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	25,018	107,070
2021	103,661	77,549
2020	60,343	37,605
2019	27,043	41,591
2018	12,370	28,814
Prior	33,239	2,418
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	261,674	295,047
Real estate loans | Construction | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	25,018	107,070
2021	103,661	77,549
2020	60,343	37,498
2019	26,936	41,591
2018	12,370	28,814
Prior	33,239	2,418
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	261,567	294,940
Real estate loans | Construction | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	107
2019	107	0
2018	0	0
Prior	0	0
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	107	107
Real estate loans | Construction | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	0
2019	0	0
2018	0	0
Prior	0	0
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	0	0
Commercial business loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	467,350	453,166
Commercial business loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	11,417	84,551
2021	61,528	36,201
2020	34,680	27,237
2019	25,969	33,123
2018	32,574	22,151
Prior	45,559	27,170
Revolving Loans	254,790	221,799
Revolving Loans to Term Loans	0	0
Total	466,517	452,232
Commercial business loans | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	11,417	84,113
2021	61,122	36,115
2020	34,612	25,156
2019	24,236	30,670
2018	28,606	21,762
Prior	44,945	26,515
Revolving Loans	246,199	210,597
Revolving Loans to Term Loans	0	0
Total	451,137	434,928
Commercial business loans | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	246
2021	235	15
2020	0	1,729
2019	1,412	1,369
2018	1,181	18
Prior	44	46
Revolving Loans	2,806	3,291
Revolving Loans to Term Loans	0	0
Total	5,678	6,714
Commercial business loans | Substandard | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	192
2021	171	71
2020	68	352
2019	321	1,084
2018	2,787	371
Prior	570	609
Revolving Loans	5,785	7,911
Revolving Loans to Term Loans	0	0
Total	9,702	10,590
Consumer loans | Home equity loans and advances
Financing Receivable, Credit Quality Indicator [Line Items]
Total	270,709	276,563
Consumer loans | Home equity loans and advances | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	7,473	22,393
2021	22,217	15,977
2020	15,097	15,906
2019	14,303	13,146
2018	12,162	12,023
Prior	104,045	101,116
Revolving Loans	94,955	95,576
Revolving Loans to Term Loans	457	426
Total	270,709	276,563
Consumer loans | Home equity loans and advances | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	7,473	22,393
2021	22,217	15,977
2020	15,097	15,906
2019	14,303	13,146
2018	12,162	12,023
Prior	103,868	100,870
Revolving Loans	94,865	95,484
Revolving Loans to Term Loans	457	426
Total	270,442	276,225
Consumer loans | Home equity loans and advances | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	0
2019	0	0
2018	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
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	0
2019	0	0
2018	0	0
Prior	177	246
Revolving Loans	90	92
Revolving Loans to Term Loans	0	0
Total	267	338
Consumer loans | Other consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total	1,659	1,428
Consumer loans | Other consumer loans | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	877	659
2021	116	58
2020	54	284
2019	229	60
2018	49	9
Prior	10	5
Revolving Loans	324	353
Revolving Loans to Term Loans	0	0
Total	1,659	1,428
Consumer loans | Other consumer loans | Pass | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	877	659
2021	116	58
2020	54	284
2019	229	60
2018	49	9
Prior	10	5
Revolving Loans	324	353
Revolving Loans to Term Loans	0	0
Total	1,659	1,428
Consumer loans | Other consumer loans | Special mention | Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	0
2019	0	0
2018	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
Financing Receivable, Credit Quality Indicator [Line Items]
2022	0	0
2021	0	0
2020	0	0
2019	0	0
2018	0	0
Prior	0	0
Revolving Loans	0	0
Revolving Loans to Term Loans	0	0
Total	$ 0	$ 0