Loans Receivable and Allowance for Credit Losses - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022		Mar. 31, 2021
Allowance for loan losses:
Balance at beginning of period	$ 62,689	[1]	$ 74,676
Provision for (reversal of) credit losses	805		(1,280)
Recoveries	168		37
Charge-offs	(57)		(1,529)
Balance at end of period	47,162	[1]	71,904
Effect of adopting ASU No. 2016-13 ("CECL")
Allowance for loan losses:
Balance at beginning of period	(16,443)
Real estate loans | One-to-four family
Allowance for loan losses:
Balance at beginning of period	8,798		13,586
Provision for (reversal of) credit losses	2,185		6,477
Recoveries	139		3
Charge-offs	0		(216)
Balance at end of period	8,814		19,850
Real estate loans | One-to-four family | Effect of adopting ASU No. 2016-13 ("CECL")
Allowance for loan losses:
Balance at beginning of period	(2,308)
Real estate loans | Multifamily
Allowance for loan losses:
Balance at beginning of period	7,741		8,897
Provision for (reversal of) credit losses	5,492		(1,942)
Recoveries	0		0
Charge-offs	0		0
Balance at end of period	11,203		6,955
Real estate loans | Multifamily | Effect of adopting ASU No. 2016-13 ("CECL")
Allowance for loan losses:
Balance at beginning of period	(2,030)
Real estate loans | Commercial real estate
Allowance for loan losses:
Balance at beginning of period	16,114		21,784
Provision for (reversal of) credit losses	1,626		(4,730)
Recoveries	0		6
Charge-offs	0		(166)
Balance at end of period	13,513		16,894
Real estate loans | Commercial real estate | Effect of adopting ASU No. 2016-13 ("CECL")
Allowance for loan losses:
Balance at beginning of period	(4,227)
Real estate loans | Construction
Allowance for loan losses:
Balance at beginning of period	8,943		11,271
Provision for (reversal of) credit losses	(1,623)		192
Recoveries	0		1
Charge-offs	0		0
Balance at end of period	4,974		11,464
Real estate loans | Construction | Effect of adopting ASU No. 2016-13 ("CECL")
Allowance for loan losses:
Balance at beginning of period	(2,346)
Commercial business loans
Allowance for loan losses:
Balance at beginning of period	20,214		17,384
Provision for (reversal of) credit losses	(7,767)		(1,509)
Recoveries	25		16
Charge-offs	(27)		(1,087)
Balance at end of period	7,143		14,804
Commercial business loans | Effect of adopting ASU No. 2016-13 ("CECL")
Allowance for loan losses:
Balance at beginning of period	(5,302)
Consumer loans | Home equity loans and advances
Allowance for loan losses:
Balance at beginning of period	873		1,748
Provision for (reversal of) credit losses	886		230
Recoveries	4		11
Charge-offs	(27)		(58)
Balance at end of period	1,507		1,931
Consumer loans | Home equity loans and advances | Effect of adopting ASU No. 2016-13 ("CECL")
Allowance for loan losses:
Balance at beginning of period	(229)
Consumer loans | Other consumer loans
Allowance for loan losses:
Balance at beginning of period	6		6
Provision for (reversal of) credit losses	6		2
Recoveries	0		0
Charge-offs	(3)		(2)
Balance at end of period	8		$ 6
Consumer loans | Other consumer loans | Effect of adopting ASU No. 2016-13 ("CECL")
Allowance for loan losses:
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.