Loans Receivable and Allowance for Credit Losses - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2022		Sep. 30, 2021	Sep. 30, 2022		Sep. 30, 2021
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	$ 50,583		$ 69,898	$ 62,689	[1]	$ 74,676
Initial allowance related to PCD loans				633
Provision for (reversal of) credit losses	1,516		480	5,004		(2,561)
Recoveries	94		347	495		1,471
Charge-offs	(302)		(399)	(487)		(3,260)
Balance at end of period	51,891	[1]	70,326	51,891	[1]	70,326
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)
Real estate loans | One-to-four family
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	10,836		17,108	8,798		13,586
Initial allowance related to PCD loans				131
Provision for (reversal of) credit losses	1,394		(2,218)	5,364		1,796
Recoveries	0		4	338		18
Charge-offs	(284)		(106)	(377)		(612)
Balance at end of period	11,946		14,788	11,946		14,788
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)
Real estate loans | Multifamily
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	10,932		8,442	7,741		8,897
Initial allowance related to PCD loans				0
Provision for (reversal of) credit losses	(3,683)		(146)	1,538		(305)
Recoveries	0		217	0		217
Charge-offs	0		0	0		(296)
Balance at end of period	7,249		8,513	7,249		8,513
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)
Real estate loans | Commercial real estate
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	14,480		17,814	16,114		21,784
Initial allowance related to PCD loans				474
Provision for (reversal of) credit losses	3,219		(171)	5,338		(4,812)
Recoveries	0		77	0		1,014
Charge-offs	0		0	0		(266)
Balance at end of period	17,699		17,720	17,699		17,720
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)
Real estate loans | Construction
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	5,570		9,160	8,943		11,271
Initial allowance related to PCD loans				3
Provision for (reversal of) credit losses	70		322	(960)		(1,790)
Recoveries	0		0	0		1
Charge-offs	0		0	0		0
Balance at end of period	5,640		9,482	5,640		9,482
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)
Commercial business loans
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	7,284		15,898	20,214		17,384
Initial allowance related to PCD loans				19
Provision for (reversal of) credit losses	120		2,854	(7,520)		2,945
Recoveries	76		42	131		169
Charge-offs	0		(69)	(62)		(1,773)
Balance at end of period	7,480		18,725	7,480		18,725
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)
Consumer loans | Home equity loans and advances
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	1,471		1,471	873		1,748
Initial allowance related to PCD loans				6
Provision for (reversal of) credit losses	385		(165)	1,225		(400)
Recoveries	18		7	26		52
Charge-offs	(6)		(221)	(33)		(308)
Balance at end of period	1,868		1,092	1,868		1,092
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)
Consumer loans | Other consumer loans
Financing Receivable, Excluding Accrued Interest, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	10		5	6		6
Initial allowance related to PCD loans				0
Provision for (reversal of) credit losses	11		4	19		5
Recoveries	0		0	0		0
Charge-offs	(12)		(3)	(15)		(5)
Balance at end of period	$ 9		$ 6	9		$ 6
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]  (1) The Company adopted ASU 2016-13 as of January 1, 2022. Prior year periods have not been restated.