Loans Receivable and Allowance for Credit Losses - Aging of Loans (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Non-accrual	$ 11,100	$ 6,700
Total gross loans	7,725,645	7,641,593
Real estate loans | One-to-four family
Financing Receivable, Past Due [Line Items]
Total gross loans	2,791,201	2,862,342
Real estate loans | Multifamily
Financing Receivable, Past Due [Line Items]
Total gross loans	1,376,999	1,239,207
Real estate loans | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total gross loans	2,399,479	2,426,510
Real estate loans | Construction
Financing Receivable, Past Due [Line Items]
Total gross loans	380,028	337,593
Commercial business loans
Financing Receivable, Past Due [Line Items]
Total gross loans	505,933	497,965
Consumer loans | Home equity loans and advances
Financing Receivable, Past Due [Line Items]
Total gross loans	269,453	274,551
Consumer loans | Other consumer loans
Financing Receivable, Past Due [Line Items]
Total gross loans	2,552	3,425
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Past Due [Line Items]
Non-accrual	11,091	6,721
Total gross loans	7,709,538	7,624,534
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	25,060	17,477
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	10,359	9,969
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	5,400	2,036
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	9,301	5,472
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	7,684,478	7,607,057
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	4,077	2,730
Total gross loans	2,789,269	2,860,184
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	13,473	7,020
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	7,826	4,063
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	3,154	1,149
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	2,493	1,808
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	2,775,796	2,853,164
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	1,376,999	1,239,207
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	2,101	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	2,101	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	1,374,898	1,239,207
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Financing Receivable, Past Due [Line Items]
Non-accrual	3,744	2,892
Total gross loans	2,386,896	2,413,394
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	5,890	3,745
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	203	0
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	1,942	853
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	3,745	2,892
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	2,381,006	2,409,649
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	378,988	336,553
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	5,218
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	5,218
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	378,988	331,335
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Financing Receivable, Past Due [Line Items]
Non-accrual	3,067	801
Total gross loans	505,524	497,469
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	3,143	694
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	0	220
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	228	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	2,915	474
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	502,381	496,775
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	203	286
Total gross loans	269,310	274,302
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	436	784
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	229	465
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	59	33
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	148	286
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	268,874	273,518
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Financing Receivable, Past Due [Line Items]
Non-accrual	0	12
Total gross loans	2,552	3,425
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	17	16
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	3
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	17	1
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	0	12
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	$ 2,535	$ 3,409