Loans Receivable and Allowance for Credit Losses - Loans Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 7,292,296	$ 6,335,722
Net deferred loan costs, fees and purchased premiums and discounts	33,927	24,879
Loans receivable	7,326,223	6,360,601
Real estate loans | One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,708,293	2,092,748
Real estate loans | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	1,142,459	1,041,108
Real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,370,524	2,175,662
Real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	290,690	295,047
Commercial business loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	498,140	453,166
Consumer loans | Home equity loans and advances
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	279,976	276,563
Consumer loans | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,214	1,428
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	7,272,525	6,328,931
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,706,114	2,092,317
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	1,142,459	1,041,108
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,354,786	2,170,236
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	289,650	295,047
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	497,478	452,232
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	279,824	276,563
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,214	1,428
Financial Asset Acquired with Credit Deterioration
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	19,771	6,791
Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,179	431
Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	0	0
Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	15,738	5,426
Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	1,040	0
Financial Asset Acquired with Credit Deterioration | Commercial business loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	662	934
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	152	0
Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 0	$ 0