Loans Receivable and Allowance for Loan Losses - Aging of Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Non-accrual	$ 3,900	$ 8,200
Total gross loans	6,335,722	6,168,892
Real estate loans | One-to-four family
Financing Receivable, Past Due [Line Items]
Total gross loans	2,092,748	1,940,636
Real estate loans | Multifamily and commercial
Financing Receivable, Past Due [Line Items]
Total gross loans	3,216,770	2,822,858
Real estate loans | Construction
Financing Receivable, Past Due [Line Items]
Total gross loans	295,047	328,711
Commercial business loans
Financing Receivable, Past Due [Line Items]
Total gross loans	453,166	754,013
Consumer loans | Home equity loans and advances
Financing Receivable, Past Due [Line Items]
Total gross loans	276,563	321,177
Consumer loans | Other consumer loans
Financing Receivable, Past Due [Line Items]
Total gross loans	1,428	1,497
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Past Due [Line Items]
Non-accrual	3,939	8,156
Total gross loans	6,328,931	6,162,547
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	10,091	31,416
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	5,840	22,766
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 60-89 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	2,033	2,664
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	2,218	5,986
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	6,318,840	6,131,131
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	1,416	2,637
Total gross loans	2,092,317	1,940,327
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	5,480	5,881
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	3,131	3,068
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	1,976	912
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	373	1,901
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	2,086,837	1,934,446
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily and commercial
Financing Receivable, Past Due [Line Items]
Non-accrual	1,561	1,873
Total gross loans	3,211,344	2,817,965
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily and commercial | Financial Asset, Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	3,750	16,883
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily and commercial | 30-59 Days
Financing Receivable, Past Due [Line Items]
Total gross loans	2,189	15,645
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily and commercial | 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 and commercial | 90 Days or More
Financing Receivable, Past Due [Line Items]
Total gross loans	1,561	1,238
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily and commercial | Financial Asset, Not Past Due
Financing Receivable, Past Due [Line Items]
Total gross loans	3,207,594	2,801,082
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	295,047	328,711
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	550
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	550
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	295,047	328,161
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Financing Receivable, Past Due [Line Items]
Non-accrual	761	2,968
Total gross loans	452,232	752,870
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	615	5,852
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	412	2,343
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	1,056
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	203	2,453
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	451,617	747,018
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	201	678
Total gross loans	276,563	321,177
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	242	2,246
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	108	1,156
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	53	696
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	81	394
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	276,321	318,931
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	1,428	1,497
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	4	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	4
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	4	0
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	$ 1,424	$ 1,493