Loans Receivable and Allowance for Credit Losses - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 53,456	$ 50,583	$ 52,803	$ 62,689	$ 62,689
Initial allowance related to PCD loans				633
Provision for (reversal of) credit losses	2,379	1,516	3,632	5,004
Recoveries	674	94	909	495
Charge-offs	(2,396)	(302)	(3,231)	(487)
Balance at end of period	54,113	51,891	54,113	51,891	52,803
Effect of adopting ASU No. 2016-13 ("CECL")
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(16,443)	(16,443)
Real estate loans | One-to-four family
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	11,026	10,836	11,802	8,798	8,798
Initial allowance related to PCD loans				131
Provision for (reversal of) credit losses	1,063	1,394	421	5,364
Recoveries	0	0	0	338
Charge-offs	(218)	(284)	(352)	(377)
Balance at end of period	11,871	11,946	11,871	11,946	11,802
Real estate loans | One-to-four family | Effect of adopting ASU No. 2016-13 ("CECL")
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(2,308)	(2,308)
Real estate loans | Multifamily
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	9,392	10,932	7,877	7,741	7,741
Initial allowance related to PCD loans				0
Provision for (reversal of) credit losses	117	(3,683)	1,632	1,538
Recoveries	0	0	0	0
Charge-offs	0	0	0	0
Balance at end of period	9,509	7,249	9,509	7,249	7,877
Real estate loans | Multifamily | Effect of adopting ASU No. 2016-13 ("CECL")
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(2,030)	(2,030)
Real estate loans | Commercial real estate
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	16,212	14,480	18,111	16,114	16,114
Initial allowance related to PCD loans				474
Provision for (reversal of) credit losses	(454)	3,219	(2,203)	5,338
Recoveries	0	0	0	0
Charge-offs	0	0	(150)	0
Balance at end of period	15,758	17,699	15,758	17,699	18,111
Real estate loans | Commercial real estate | Effect of adopting ASU No. 2016-13 ("CECL")
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(4,227)	(4,227)
Real estate loans | Construction
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	6,935	5,570	6,425	8,943	8,943
Initial allowance related to PCD loans				3
Provision for (reversal of) credit losses	10	70	520	(960)
Recoveries	0	0	0	0
Charge-offs	0	0	0	0
Balance at end of period	6,945	5,640	6,945	5,640	6,425
Real estate loans | Construction | Effect of adopting ASU No. 2016-13 ("CECL")
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(2,346)	(2,346)
Commercial business loans
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	7,690	7,284	6,897	20,214	20,214
Initial allowance related to PCD loans				19
Provision for (reversal of) credit losses	1,688	120	2,725	(7,520)
Recoveries	624	76	830	131
Charge-offs	(2,168)	0	(2,618)	(62)
Balance at end of period	7,834	7,480	7,834	7,480	6,897
Commercial business loans | Effect of adopting ASU No. 2016-13 ("CECL")
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(5,302)	(5,302)
Consumer loans | Home equity loans and advances
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	2,193	1,471	1,681	873	873
Initial allowance related to PCD loans				6
Provision for (reversal of) credit losses	(53)	385	460	1,225
Recoveries	49	18	73	26
Charge-offs	0	(6)	(25)	(33)
Balance at end of period	2,189	1,868	2,189	1,868	1,681
Consumer loans | Home equity loans and advances | Effect of adopting ASU No. 2016-13 ("CECL")
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				(229)	(229)
Consumer loans | Other consumer loans
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	8	10	10	6	6
Initial allowance related to PCD loans				0
Provision for (reversal of) credit losses	8	11	77	19
Recoveries	1	0	6	0
Charge-offs	(10)	(12)	(86)	(15)
Balance at end of period	$ 7	$ 9	$ 7	9	10
Consumer loans | Other consumer loans | Effect of adopting ASU No. 2016-13 ("CECL")
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period				$ (1)	$ (1)