Loans Receivable and Allowance for Credit Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Allowance for credit losses:
Allowance for credit losses on loans	$ 55,401	$ 55,096	$ 52,873	$ 52,803
Total loans:
Total loans	7,780,637	7,839,754
Real estate loans | One-to-four family
Allowance for credit losses:
Allowance for credit losses on loans	13,840	13,017	12,789	11,802
Total loans:
Total loans	2,780,805	2,794,726
Real estate loans | Multifamily
Allowance for credit losses:
Allowance for credit losses on loans	8,670	8,742	8,145	7,877
Total loans:
Total loans	1,429,369	1,409,187
Real estate loans | Commercial real estate
Allowance for credit losses:
Allowance for credit losses on loans	15,232	15,757	16,257	18,111
Total loans:
Total loans	2,330,769	2,389,766
Real estate loans | Construction
Allowance for credit losses:
Allowance for credit losses on loans	8,068	7,758	6,739	6,425
Total loans:
Total loans	437,566	443,094
Commercial business loans
Allowance for credit losses:
Allowance for credit losses on loans	7,711	7,923	7,320	6,897
Total loans:
Total loans	538,604	533,410
Consumer loans | Home equity loans and advances
Allowance for credit losses:
Allowance for credit losses on loans	1,873	1,892	1,614	1,681
Total loans:
Total loans	260,923	266,770
Consumer loans | Other consumer loans
Allowance for credit losses:
Allowance for credit losses on loans	7	7	$ 9	$ 10
Total loans:
Total loans	2,601	2,801
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Individually analyzed loans	359	614
Collectively analyzed loans	54,975	54,309
Total loans:
Individually analyzed loans	20,694	31,956
Collectively analyzed loans	7,744,998	7,792,709
Total loans	7,765,692	7,824,665
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Individually analyzed loans	35	186
Collectively analyzed loans	13,800	12,827
Total loans:
Individually analyzed loans	1,728	4,063
Collectively analyzed loans	2,777,204	2,788,770
Total loans	2,778,932	2,792,833
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Allowance for credit losses:
Individually analyzed loans	0	7
Collectively analyzed loans	8,670	8,735
Total loans:
Individually analyzed loans	46	382
Collectively analyzed loans	1,429,323	1,408,805
Total loans	1,429,369	1,409,187
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Allowance for credit losses:
Individually analyzed loans	226	237
Collectively analyzed loans	14,947	15,378
Total loans:
Individually analyzed loans	9,695	15,360
Collectively analyzed loans	2,308,483	2,361,717
Total loans	2,318,178	2,377,077
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for credit losses:
Individually analyzed loans	0	0
Collectively analyzed loans	8,068	7,758
Total loans:
Individually analyzed loans	0	0
Collectively analyzed loans	437,566	443,094
Total loans	437,566	443,094
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Individually analyzed loans	98	154
Collectively analyzed loans	7,611	7,742
Total loans:
Individually analyzed loans	9,115	11,550
Collectively analyzed loans	529,145	521,491
Total loans	538,260	533,041
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Individually analyzed loans	0	30
Collectively analyzed loans	1,872	1,862
Total loans:
Individually analyzed loans	110	601
Collectively analyzed loans	260,676	266,031
Total loans	260,786	266,632
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Allowance for credit losses:
Individually analyzed loans	0	0
Collectively analyzed loans	7	7
Total loans:
Individually analyzed loans	0	0
Collectively analyzed loans	2,601	2,801
Total loans	2,601	2,801
Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Allowance for credit losses on loans	67	173
Total loans:
Total loans	14,945	15,089
Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Allowance for credit losses on loans	5	4
Total loans:
Total loans	1,873	1,893
Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Allowance for credit losses:
Allowance for credit losses on loans	0	0
Total loans:
Total loans	0	0
Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Allowance for credit losses:
Allowance for credit losses on loans	59	142
Total loans:
Total loans	12,591	12,689
Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for credit losses:
Allowance for credit losses on loans	0	0
Total loans:
Total loans	0	0
Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Allowance for credit losses on loans	2	27
Total loans:
Total loans	344	369
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Allowance for credit losses on loans	1	0
Total loans:
Total loans	137	138
Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Allowance for credit losses:
Allowance for credit losses on loans	0	0
Total loans:
Total loans	$ 0	$ 0