Loans Receivable and Allowance for Credit Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Sep. 30, 2022		Jun. 30, 2022	Dec. 31, 2021		Sep. 30, 2021	Jun. 30, 2021	Dec. 31, 2020
Allowance for credit losses:
Total	$ 51,891	[1]	$ 50,583	$ 62,689	[1]	$ 70,326	$ 69,898	$ 74,676
Total loans:
Total	7,292,296			6,335,722
Real estate loans | One-to-four family
Allowance for credit losses:
Total	11,946		10,836	8,798		14,788	17,108	13,586
Total loans:
Total	2,708,293			2,092,748
Real estate loans | Multifamily
Allowance for credit losses:
Total	7,249		10,932	7,741		8,513	8,442	8,897
Total loans:
Total	1,142,459			1,041,108
Real estate loans | Commercial real estate
Allowance for credit losses:
Total	17,699		14,480	16,114		17,720	17,814	21,784
Total loans:
Total	2,370,524			2,175,662
Real estate loans | Construction
Allowance for credit losses:
Total	5,640		5,570	8,943		9,482	9,160	11,271
Total loans:
Total	290,690			295,047
Commercial business loans
Allowance for credit losses:
Total	7,480		7,284	20,214		18,725	15,898	17,384
Total loans:
Total	498,140			453,166
Consumer loans | Home equity loans and advances
Allowance for credit losses:
Total	1,868		1,471	873		1,092	1,471	1,748
Total loans:
Total	279,976			276,563
Consumer loans | Other consumer loans
Allowance for credit losses:
Total	9		$ 10	6		$ 6	$ 5	$ 6
Total loans:
Total	2,214			1,428
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Individually evaluated for impairment	330			378
Collectively evaluated for impairment	51,474			62,311
Total loans:
Individually evaluated for impairment	23,466			24,287
Collectively evaluated for impairment	7,249,059			6,304,644
Total	7,272,525			6,328,931
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Individually evaluated for impairment	213			258
Collectively evaluated for impairment	11,725			8,540
Total loans:
Individually evaluated for impairment	4,223			5,184
Collectively evaluated for impairment	2,701,891			2,087,133
Total	2,706,114			2,092,317
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Allowance for credit losses:
Individually evaluated for impairment	3			0
Collectively evaluated for impairment	7,246			7,741
Total loans:
Individually evaluated for impairment	475			762
Collectively evaluated for impairment	1,141,984			1,040,346
Total	1,142,459			1,041,108
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Allowance for credit losses:
Individually evaluated for impairment	98			97
Collectively evaluated for impairment	17,540			16,017
Total loans:
Individually evaluated for impairment	16,836			15,830
Collectively evaluated for impairment	2,337,950			2,154,406
Total	2,354,786			2,170,236
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for credit losses:
Individually evaluated for impairment	0			0
Collectively evaluated for impairment	5,630			8,943
Total loans:
Individually evaluated for impairment	0			0
Collectively evaluated for impairment	289,650			295,047
Total	289,650			295,047
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Individually evaluated for impairment	10			16
Collectively evaluated for impairment	7,463			20,198
Total loans:
Individually evaluated for impairment	1,237			1,806
Collectively evaluated for impairment	496,241			450,426
Total	497,478			452,232
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Individually evaluated for impairment	6			7
Collectively evaluated for impairment	1,861			866
Total loans:
Individually evaluated for impairment	695			705
Collectively evaluated for impairment	279,129			275,858
Total	279,824			276,563
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Allowance for credit losses:
Individually evaluated for impairment	0			0
Collectively evaluated for impairment	9			6
Total loans:
Individually evaluated for impairment	0			0
Collectively evaluated for impairment	2,214			1,428
Total	2,214			1,428
Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Total	87			0
Total loans:
Total	19,771			6,791
Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Total	8			0
Total loans:
Total	2,179			431
Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily
Allowance for credit losses:
Total	0			0
Total loans:
Total	0			0
Financial Asset Acquired with Credit Deterioration | Real estate loans | Commercial real estate
Allowance for credit losses:
Total	61			0
Total loans:
Total	15,738			5,426
Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for credit losses:
Total	10			0
Total loans:
Total	1,040			0
Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Total	7			0
Total loans:
Total	662			934
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Total	1			0
Total loans:
Total	152			0
Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Allowance for credit losses:
Total	0			0
Total loans:
Total	$ 0			$ 0

[1]  (1) The Company adopted ASU 2016-13 as of January 1, 2022. Prior year periods have not been restated.