Loans Receivable and Allowance for Credit Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2022		Mar. 31, 2022	Dec. 31, 2021		Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Allowance for credit losses:
Total	$ 50,583	[1]	$ 47,162	$ 62,689	[1]	$ 69,898	$ 71,904	$ 74,676
Total loans:
Total	6,951,786			6,335,722
Real estate loans | One-to-four family
Allowance for credit losses:
Total	10,836		8,814	8,798		17,108	19,850	13,586
Total loans:
Total	2,515,059			2,092,748
Real estate loans | Multifamily
Allowance for credit losses:
Total	10,932		11,203	7,741		8,442	6,955	8,897
Total loans:
Total	1,077,459			1,041,108
Real estate loans | Commercial real estate
Allowance for credit losses:
Total	14,480		13,513	16,114		17,814	16,894	21,784
Total loans:
Total	2,322,757			2,175,662
Real estate loans | Construction
Allowance for credit losses:
Total	5,570		4,974	8,943		9,160	11,464	11,271
Total loans:
Total	277,750			295,047
Commercial business loans
Allowance for credit losses:
Total	7,284		7,143	20,214		15,898	14,804	17,384
Total loans:
Total	474,844			453,166
Consumer loans | Home equity loans and advances
Allowance for credit losses:
Total	1,471		1,507	873		1,471	1,931	1,748
Total loans:
Total	281,786			276,563
Consumer loans | Other consumer loans
Allowance for credit losses:
Total	10		$ 8	6		$ 5	$ 6	$ 6
Total loans:
Total	2,131			1,428
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Individually evaluated for impairment	385			378
Collectively evaluated for impairment	50,121			62,311
Total loans:
Individually evaluated for impairment	22,494			24,287
Collectively evaluated for impairment	6,907,939			6,304,644
Total	6,930,433			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	246			258
Collectively evaluated for impairment	10,580			8,540
Total loans:
Individually evaluated for impairment	4,278			5,184
Collectively evaluated for impairment	2,507,437			2,087,133
Total	2,511,715			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	4			0
Collectively evaluated for impairment	10,928			7,741
Total loans:
Individually evaluated for impairment	720			762
Collectively evaluated for impairment	1,076,739			1,040,346
Total	1,077,459			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	97			97
Collectively evaluated for impairment	14,331			16,017
Total loans:
Individually evaluated for impairment	15,337			15,830
Collectively evaluated for impairment	2,291,346			2,154,406
Total	2,306,683			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	5,560			8,943
Total loans:
Individually evaluated for impairment	0			0
Collectively evaluated for impairment	276,710			295,047
Total	276,710			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	7,269			20,198
Total loans:
Individually evaluated for impairment	1,300			1,806
Collectively evaluated for impairment	472,845			450,426
Total	474,145			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	28			7
Collectively evaluated for impairment	1,443			866
Total loans:
Individually evaluated for impairment	859			705
Collectively evaluated for impairment	280,731			275,858
Total	281,590			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	10			6
Total loans:
Individually evaluated for impairment	0			0
Collectively evaluated for impairment	2,131			1,428
Total	2,131			1,428
Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Total	77			0
Total loans:
Total	21,353			6,791
Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Total	10			0
Total loans:
Total	3,344			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	52			0
Total loans:
Total	16,074			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	5			0
Total loans:
Total	699			934
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Total	0			0
Total loans:
Total	196			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.