Loans Receivable and Allowance for Credit Losses - Aging of Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Financing Receivable, Past Due [Line Items]
Non-accrual	$ 7,000	$ 3,900
Total gross loans	7,292,296	6,335,722
Real estate loans | One-to-four family
Financing Receivable, Past Due [Line Items]
Total gross loans	2,708,293	2,092,748
Real estate loans | Multifamily
Financing Receivable, Past Due [Line Items]
Total gross loans	1,142,459	1,041,108
Real estate loans | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total gross loans	2,370,524	2,175,662
Real estate loans | Construction
Financing Receivable, Past Due [Line Items]
Total gross loans	290,690	295,047
Commercial business loans
Financing Receivable, Past Due [Line Items]
Total gross loans	498,140	453,166
Consumer loans | Home equity loans and advances
Financing Receivable, Past Due [Line Items]
Total gross loans	279,976	276,563
Consumer loans | Other consumer loans
Financing Receivable, Past Due [Line Items]
Total gross loans	2,214	1,428
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Past Due [Line Items]
Non-accrual	6,996	3,939
Total gross loans	7,272,525	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	16,684	10,091
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	9,598	5,840
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	1,938	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	5,148	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	7,255,841	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	2,518	1,416
Total gross loans	2,706,114	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	8,241	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	5,101	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	1,883	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	1,257	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	2,697,873	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	1,142,459	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	1,092	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	1,092	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	1,141,367	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	3,373	1,561
Total gross loans	2,354,786	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	4,328	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	1,436	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	0	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	2,892	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	2,350,458	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	289,650	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	544	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	544	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	289,106	295,047
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Financing Receivable, Past Due [Line Items]
Non-accrual	906	761
Total gross loans	497,478	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	840	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	0	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	840	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	496,638	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	199	201
Total gross loans	279,824	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	1,624	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	1,425	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	40	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	159	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	278,200	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	2,214	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	15	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	15	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	0	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	$ 2,199	$ 1,424