Loans Receivable and Allowance for Credit Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Allowance for credit losses:
Allowance for credit losses on loans	$ 58,495	$ 57,062	$ 55,096	$ 54,113	$ 53,456	$ 52,803
Total loans:
Total loans	7,821,548		7,839,754
Commercial real estate | One-to-four family
Allowance for credit losses:
Allowance for credit losses on loans	12,841	14,888	13,017	11,871	11,026	11,802
Total loans:
Total loans	2,739,024		2,794,726
Commercial real estate | Multifamily
Allowance for credit losses:
Allowance for credit losses on loans	8,515	8,391	8,742	9,509	9,392	7,877
Total loans:
Total loans	1,399,000		1,409,187
Commercial real estate | Commercial real estate
Allowance for credit losses:
Allowance for credit losses on loans	15,556	15,080	15,757	15,758	16,212	18,111
Total loans:
Total loans	2,322,262		2,389,766
Commercial real estate | Construction
Allowance for credit losses:
Allowance for credit losses on loans	7,076	8,549	7,758	6,945	6,935	6,425
Total loans:
Total loans	510,439		443,094
Commercial business loans | Commercial Business
Allowance for credit losses:
Allowance for credit losses on loans	13,115	7,494	7,923	7,834	7,690	6,897
Total loans:
Total loans	586,758		533,410
Consumer loans | Home equity loans and advances
Allowance for credit losses:
Allowance for credit losses on loans	1,384	2,654	1,892	2,189	2,193	1,681
Total loans:
Total loans	261,188		266,770
Consumer loans | Other consumer loans
Allowance for credit losses:
Allowance for credit losses on loans	8	$ 6	7	$ 7	$ 8	$ 10
Total loans:
Total loans	2,877		2,801
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Individually analyzed loans	0		614
Collectively analyzed loans	58,462		54,309
Total loans:
Individually analyzed loans	32,792		31,956
Collectively analyzed loans	7,776,961		7,792,709
Total loans	7,809,753		7,824,665
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial real estate | One-to-four family
Allowance for credit losses:
Individually analyzed loans	0		186
Collectively analyzed loans	12,837		12,827
Total loans:
Individually analyzed loans	7,238		4,063
Collectively analyzed loans	2,729,952		2,788,770
Total loans	2,737,190		2,792,833
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial real estate | Multifamily
Allowance for credit losses:
Individually analyzed loans	0		7
Collectively analyzed loans	8,515		8,735
Total loans:
Individually analyzed loans	5,743		382
Collectively analyzed loans	1,393,257		1,408,805
Total loans	1,399,000		1,409,187
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial real estate | Commercial real estate
Allowance for credit losses:
Individually analyzed loans	0		237
Collectively analyzed loans	15,527		15,378
Total loans:
Individually analyzed loans	7,578		15,360
Collectively analyzed loans	2,305,181		2,361,717
Total loans	2,312,759		2,377,077
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial real estate | Construction
Allowance for credit losses:
Individually analyzed loans	0		0
Collectively analyzed loans	7,076		7,758
Total loans:
Individually analyzed loans	0		0
Collectively analyzed loans	510,439		443,094
Total loans	510,439		443,094
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Total loans:
Total loans	586,447		533,041
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans | Commercial Business
Allowance for credit losses:
Individually analyzed loans	0		154
Collectively analyzed loans	13,115		7,742
Total loans:
Individually analyzed loans	12,062		11,550
Collectively analyzed loans	574,385		521,491
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	1,384		1,862
Total loans:
Individually analyzed loans	171		601
Collectively analyzed loans	260,870		266,031
Total loans	261,041		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	8		7
Total loans:
Individually analyzed loans	0		0
Collectively analyzed loans	2,877		2,801
Total loans	2,877		2,801
Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Allowance for credit losses on loans	33		173
Total loans:
Total loans	11,795		15,089
Financial Asset Acquired with Credit Deterioration | Commercial real estate | One-to-four family
Allowance for credit losses:
Allowance for credit losses on loans	4		4
Total loans:
Total loans	1,834		1,893
Financial Asset Acquired with Credit Deterioration | Commercial real estate | 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 | Commercial real estate | Commercial real estate
Allowance for credit losses:
Allowance for credit losses on loans	29		142
Total loans:
Total loans	9,503		12,689
Financial Asset Acquired with Credit Deterioration | Commercial real estate | 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 | Commercial Business
Allowance for credit losses:
Allowance for credit losses on loans	0		27
Total loans:
Total loans	311		369
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Allowance for credit losses on loans	0		0
Total loans:
Total loans	147		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