Loans Receivable and Allowance for Credit Losses - Aging of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Non-accrual	$ 4,500	$ 3,900
Total gross loans	6,951,786	6,335,722
Real estate loans | One-to-four family
Financing Receivable, Past Due [Line Items]
Total gross loans	2,515,059	2,092,748
Real estate loans | Multifamily
Financing Receivable, Past Due [Line Items]
Total gross loans	1,077,459	1,041,108
Real estate loans | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total gross loans	2,322,757	2,175,662
Real estate loans | Construction
Financing Receivable, Past Due [Line Items]
Total gross loans	277,750	295,047
Commercial business loans
Financing Receivable, Past Due [Line Items]
Total gross loans	474,844	453,166
Consumer loans | Home equity loans and advances
Financing Receivable, Past Due [Line Items]
Total gross loans	281,786	276,563
Consumer loans | Other consumer loans
Financing Receivable, Past Due [Line Items]
Total gross loans	2,131	1,428
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Past Due [Line Items]
Non-accrual	4,525	3,939
Total gross loans	6,930,433	6,328,931
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	14,954	10,091
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	8,672	5,840
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	3,442	2,033
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	2,840	2,218
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	6,915,479	6,318,840
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Financing Receivable, Past Due [Line Items]
Non-accrual	2,267	1,416
Total gross loans	2,511,715	2,092,317
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	6,688	5,480
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	4,237	3,131
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	1,785	1,976
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	666	373
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	2,505,027	2,086,837
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Financing Receivable, Past Due [Line Items]
Non-accrual	0	0
Total gross loans	1,077,459	1,041,108
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	1,077,459	1,041,108
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Financing Receivable, Past Due [Line Items]
Non-accrual	1,774	1,561
Total gross loans	2,306,683	2,170,236
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	6,944	3,750
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	3,563	2,189
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	1,607	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	1,774	1,561
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	2,299,739	2,166,486
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Financing Receivable, Past Due [Line Items]
Non-accrual	0	0
Total gross loans	276,710	295,047
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	276,710	295,047
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Financing Receivable, Past Due [Line Items]
Non-accrual	318	761
Total gross loans	474,145	452,232
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	705	615
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	455	412
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	250	203
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	473,440	451,617
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Financing Receivable, Past Due [Line Items]
Non-accrual	166	201
Total gross loans	281,590	276,563
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	603	242
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	417	108
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	50	53
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	136	81
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	280,987	276,321
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Financing Receivable, Past Due [Line Items]
Non-accrual	0	0
Total gross loans	2,131	1,428
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	14	4
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	0	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	0	4
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	14	0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	$ 2,117	$ 1,424