Loans Receivable and Allowance for Credit Losses - Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2022		Dec. 31, 2021		Mar. 31, 2021	Dec. 31, 2020
Allowance for credit losses:
Total	$ 47,162	[1]	$ 62,689	[1]	$ 71,904	$ 74,676
Total loans:
Total	6,448,554		6,335,722
Real estate loans | One-to-four family
Allowance for credit losses:
Total	8,814		8,798		19,850	13,586
Total loans:
Total	2,180,121		2,092,748
Real estate loans | Multifamily
Allowance for credit losses:
Total	11,203		7,741		6,955	8,897
Total loans:
Total	1,077,938		1,041,108
Real estate loans | Commercial real estate
Allowance for credit losses:
Total	13,513		16,114		16,894	21,784
Total loans:
Total	2,189,103		2,175,662
Real estate loans | Construction
Allowance for credit losses:
Total	4,974		8,943		11,464	11,271
Total loans:
Total	261,674		295,047
Commercial business loans
Allowance for credit losses:
Total	7,143		20,214		14,804	17,384
Total loans:
Total	467,350		453,166
Consumer loans | Home equity loans and advances
Allowance for credit losses:
Total	1,507		873		1,931	1,748
Total loans:
Total	270,709		276,563
Consumer loans | Other consumer loans
Allowance for credit losses:
Total	8		6		$ 6	$ 6
Total loans:
Total	1,659		1,428
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Individually evaluated for impairment	397		378
Collectively evaluated for impairment	46,716		62,311
Total loans:
Individually evaluated for impairment	24,962		24,287
Collectively evaluated for impairment	6,416,937		6,304,644
Total	6,441,899		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	255		258
Collectively evaluated for impairment	8,557		8,540
Total loans:
Individually evaluated for impairment	4,876		5,184
Collectively evaluated for impairment	2,174,822		2,087,133
Total	2,179,698		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	5		0
Collectively evaluated for impairment	11,198		7,741
Total loans:
Individually evaluated for impairment	741		762
Collectively evaluated for impairment	1,077,197		1,040,346
Total	1,077,938		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	13,384		16,017
Total loans:
Individually evaluated for impairment	17,014		15,830
Collectively evaluated for impairment	2,166,690		2,154,406
Total	2,183,704		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	4,974		8,943
Total loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	261,674		295,047
Total	261,674		295,047
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Individually evaluated for impairment	11		16
Collectively evaluated for impairment	7,117		20,198
Total loans:
Individually evaluated for impairment	1,444		1,806
Collectively evaluated for impairment	465,073		450,426
Total	466,517		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	29		7
Collectively evaluated for impairment	1,478		866
Total loans:
Individually evaluated for impairment	887		705
Collectively evaluated for impairment	269,822		275,858
Total	270,709		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	8		6
Total loans:
Individually evaluated for impairment	0		0
Collectively evaluated for impairment	1,659		1,428
Total	1,659		1,428
Financial Asset Acquired with Credit Deterioration
Allowance for credit losses:
Total	49		0
Total loans:
Total	6,655		6,791
Financial Asset Acquired with Credit Deterioration | Real estate loans | One-to-four family
Allowance for credit losses:
Total	2		0
Total loans:
Total	423		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	32		0
Total loans:
Total	5,399		5,426
Financial Asset Acquired with Credit Deterioration | Real estate loans | Construction
Allowance for credit losses:
Total	0		0
Total loans:
Total	0		0
Financial Asset Acquired with Credit Deterioration | Commercial business loans
Allowance for credit losses:
Total	15		0
Total loans:
Total	833		934
Financial Asset Acquired with Credit Deterioration | Consumer loans | Home equity loans and advances
Allowance for credit losses:
Total	0		0
Total loans:
Total	0		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.