Loans Receivable and Allowance for Credit Losses - Aging of Loans (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Financing Receivable, Past Due [Line Items]
Non-accrual	$ 6,600	$ 6,700
Total gross loans	7,751,328	7,641,593
Real estate loans | One-to-four family
Financing Receivable, Past Due [Line Items]
Total gross loans	2,862,917	2,862,342
Real estate loans | Multifamily
Financing Receivable, Past Due [Line Items]
Total gross loans	1,315,143	1,239,207
Real estate loans | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total gross loans	2,406,590	2,426,510
Real estate loans | Construction
Financing Receivable, Past Due [Line Items]
Total gross loans	375,474	337,593
Commercial business loans
Financing Receivable, Past Due [Line Items]
Total gross loans	517,116	497,965
Consumer loans | Home equity loans and advances
Financing Receivable, Past Due [Line Items]
Total gross loans	271,766	274,551
Consumer loans | Other consumer loans
Financing Receivable, Past Due [Line Items]
Total gross loans	2,322	3,425
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Past Due [Line Items]
Non-accrual	6,610	6,721
Total gross loans	7,735,083	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	16,159	17,477
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	8,221	9,969
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	3,120	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	4,818	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	7,718,924	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	2,793	2,730
Total gross loans	2,860,964	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	8,398	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	4,873	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	2,188	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	1,337	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	2,852,566	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	1,315,143	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	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	1,315,143	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	2,892	2,892
Total gross loans	2,393,918	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	4,678	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	934	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	852	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	2,892	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	2,389,240	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	374,434	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	1,910	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	1,910	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	372,524	331,335
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Financing Receivable, Past Due [Line Items]
Non-accrual	784	801
Total gross loans	516,682	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	474	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	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	474	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	516,208	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	141	286
Total gross loans	271,620	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	699	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	504	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	80	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	115	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	270,921	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	2,322	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	0	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	0	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	$ 2,322	$ 3,409