Loans Receivable and Allowance for Credit Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Dec. 31, 2021
Allowance for credit losses:
Allowance for credit losses on loans	$ 54,113	$ 53,456	$ 52,803	$ 51,891	$ 50,583	$ 62,689
Total loans:
Total loans	7,806,180		7,641,593
Real estate loans | One-to-four family
Allowance for credit losses:
Allowance for credit losses on loans	11,871	11,026	11,802	11,946	10,836	8,798
Total loans:
Total loans	2,793,852		2,862,342
Real estate loans | Multifamily
Allowance for credit losses:
Allowance for credit losses on loans	9,509	9,392	7,877	7,249	10,932	7,741
Total loans:
Total loans	1,417,233		1,239,207
Real estate loans | Commercial real estate
Allowance for credit losses:
Allowance for credit losses on loans	15,758	16,212	18,111	17,699	14,480	16,114
Total loans:
Total loans	2,386,237		2,426,510
Real estate loans | Construction
Allowance for credit losses:
Allowance for credit losses on loans	6,945	6,935	6,425	5,640	5,570	8,943
Total loans:
Total loans	391,979		337,593
Commercial business loans
Allowance for credit losses:
Allowance for credit losses on loans	7,834	7,690	6,897	7,480	7,284	20,214
Total loans:
Total loans	547,138		497,965
Consumer loans | Home equity loans and advances
Allowance for credit losses:
Allowance for credit losses on loans	2,189	2,193	1,681	1,868	1,471	873
Total loans:
Total loans	267,155		274,551
Consumer loans | Other consumer loans
Allowance for credit losses:
Allowance for credit losses on loans	7	$ 8	10	$ 9	$ 10	$ 6
Total loans:
Total loans	2,586		3,425
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Individually analyzed loans	631		339
Collectively analyzed loans	53,315		52,381
Total loans:
Individually analyzed loans	33,439		23,220
Collectively analyzed loans	7,757,513		7,601,314
Total loans	7,790,952		7,624,534
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Individually analyzed loans	186		201
Collectively analyzed loans	11,681		11,591
Total loans:
Individually analyzed loans	3,967		4,164
Collectively analyzed loans	2,787,972		2,856,020
Total loans	2,791,939		2,860,184
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Allowance for credit losses:
Individually analyzed loans	2		3
Collectively analyzed loans	9,507		7,874
Total loans:
Individually analyzed loans	401		457
Collectively analyzed loans	1,416,832		1,238,750
Total loans	1,417,233		1,239,207
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Allowance for credit losses:
Individually analyzed loans	307		99
Collectively analyzed loans	15,311		17,961
Total loans:
Individually analyzed loans	16,768		16,729
Collectively analyzed loans	2,357,720		2,396,665
Total loans	2,374,488		2,413,394
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	6,945		6,415
Total loans:
Individually analyzed loans	0		0
Collectively analyzed loans	390,940		336,553
Total loans	390,940		336,553
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Individually analyzed loans	107		10
Collectively analyzed loans	7,704		6,876
Total loans:
Individually analyzed loans	11,692		1,173
Collectively analyzed loans	535,058		496,296
Total loans	546,750		497,469
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Individually analyzed loans	29		26
Collectively analyzed loans	2,160		1,654
Total loans:
Individually analyzed loans	611		697
Collectively analyzed loans	266,405		273,605
Total loans	267,016		274,302
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		10
Total loans:
Individually analyzed loans	0		0
Collectively analyzed loans	2,586		3,425
Total loans	2,586		3,425
Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Allowance for credit losses on loans	167		83
Total loans:
Total loans	15,228		17,059
Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Allowance for credit losses on loans	4		10
Total loans:
Total loans	1,913		2,158
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	140		51
Total loans:
Total loans	11,749		13,116
Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for credit losses:
Allowance for credit losses on loans	0		10
Total loans:
Total loans	1,039		1,040
Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Allowance for credit losses on loans	23		11
Total loans:
Total loans	388		496
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Allowance for credit losses on loans	0		1
Total loans:
Total loans	139		249
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