Loans Receivable and Allowance for Loan Losses - Allowance for Loan Losses (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for loan losses:
Total	$ 62,689	$ 74,676	$ 61,709	$ 62,342
Total loans:
Total	6,335,722	6,168,892
Real estate loans | One-to-four family
Allowance for loan losses:
Total	8,798	13,586	13,780	15,232
Total loans:
Total	2,092,748	1,940,636
Real estate loans | Multifamily and commercial
Allowance for loan losses:
Total	23,855	30,681	22,980	23,251
Total loans:
Total	3,216,770	2,822,858
Real estate loans | Construction
Allowance for loan losses:
Total	8,943	11,271	7,435	7,217
Total loans:
Total	295,047	328,711
Commercial business loans
Allowance for loan losses:
Total	20,214	17,384	15,836	14,176
Total loans:
Total	453,166	754,013
Consumer loans | Home equity loans and advances
Allowance for loan losses:
Total	873	1,748	1,669	2,458
Total loans:
Total	276,563	321,177
Consumer loans | Other consumer loans
Allowance for loan losses:
Total	6	6	$ 9	$ 8
Total loans:
Total	1,428	1,497
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Allowance for loan losses:
Individually evaluated for impairment	378	1,088
Collectively evaluated for impairment	62,311	73,588
Total loans:
Individually evaluated for impairment	24,287	45,147
Collectively evaluated for impairment	6,304,644	6,117,400
Total	6,328,931	6,162,547
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for loan losses:
Individually evaluated for impairment	258	391
Collectively evaluated for impairment	8,540	13,195
Total loans:
Individually evaluated for impairment	5,184	7,257
Collectively evaluated for impairment	2,087,133	1,933,070
Total	2,092,317	1,940,327
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily and commercial
Allowance for loan losses:
Individually evaluated for impairment	97	601
Collectively evaluated for impairment	23,758	30,080
Total loans:
Individually evaluated for impairment	16,592	32,792
Collectively evaluated for impairment	3,194,752	2,785,173
Total	3,211,344	2,817,965
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	8,943	11,271
Total loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	295,047	328,711
Total	295,047	328,711
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for loan losses:
Individually evaluated for impairment	16	84
Collectively evaluated for impairment	20,198	17,300
Total loans:
Individually evaluated for impairment	1,806	3,447
Collectively evaluated for impairment	450,426	749,423
Total	452,232	752,870
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for loan losses:
Individually evaluated for impairment	7	12
Collectively evaluated for impairment	866	1,736
Total loans:
Individually evaluated for impairment	705	1,651
Collectively evaluated for impairment	275,858	319,526
Total	276,563	321,177
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Allowance for loan losses:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	6	6
Total loans:
Individually evaluated for impairment	0	0
Collectively evaluated for impairment	1,428	1,497
Total	1,428	1,497
Financial Asset Acquired with Credit Deterioration
Allowance for loan losses:
Total	0	0
Total loans:
Total	6,791	6,345
Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for loan losses:
Total	0	0
Total loans:
Total	431	309
Financial Asset Acquired with Credit Deterioration | Real estate loans | Multifamily and commercial
Allowance for loan losses:
Total	0	0
Total loans:
Total	5,426	4,893
Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for loan losses:
Total	0	0
Total loans:
Total	0	0
Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for loan losses:
Total	0	0
Total loans:
Total	934	1,143
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for loan losses:
Total	0	0
Total loans:
Total	0	0
Financial Asset Acquired with Credit Deterioration | Consumer loans | Other consumer loans
Allowance for loan losses:
Total	0	0
Total loans:
Total	$ 0	$ 0