Loans Receivable and Allowance for Loan Losses - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Allowance for loan losses:
Beginning balance	$ 71,200	$ 62,771	$ 61,709	$ 62,342
Provision for loan losses	5,736	112	15,304	548
Recoveries	263	58	361	399
Charge-offs	(3,184)	(538)	(3,359)	(886)
Ending balance	74,015	62,403	74,015	62,403
Real estate loans \| One-to-four family
Allowance for loan losses:
Beginning balance	16,798	17,375	13,780	15,232
Provision for loan losses	(51)	(1,254)	3,050	868
Recoveries	239	4	242	25
Charge-offs	(353)	(515)	(439)	(515)
Ending balance	16,633	15,610	16,633	15,610
Real estate loans \| Multifamily and commercial
Allowance for loan losses:
Beginning balance	26,085	20,986	22,980	23,251
Provision for loan losses	1,243	1,693	4,339	(572)
Recoveries	2	0	12	0
Charge-offs	0	0	(1)	0
Ending balance	27,330	22,679	27,330	22,679
Real estate loans \| Construction
Allowance for loan losses:
Beginning balance	9,399	9,033	7,435	7,217
Provision for loan losses	817	(228)	2,781	1,588
Recoveries	1	1	1	1
Charge-offs	0	0	0	0
Ending balance	10,217	8,806	10,217	8,806
Commercial business loans
Allowance for loan losses:
Beginning balance	17,191	12,225	15,836	14,176
Provision for loan losses	3,911	441	5,258	(1,555)
Recoveries	12	53	83	366
Charge-offs	(2,800)	(1)	(2,863)	(269)
Ending balance	18,314	12,718	18,314	12,718
Consumer loans \| Home equity loans and advances
Allowance for loan losses:
Beginning balance	1,718	3,146	1,669	2,458
Provision for loan losses	(183)	(542)	(124)	219
Recoveries	9	0	23	7
Charge-offs	(30)	(21)	(54)	(101)
Ending balance	1,514	2,583	1,514	2,583
Consumer loans \| Other consumer loans
Allowance for loan losses:
Beginning balance	9	6	9	8
Provision for loan losses	(1)	2	0	0
Recoveries	0	0	0	0
Charge-offs	(1)	(1)	(2)	(1)
Ending balance	7	7	7	7
Unallocated
Allowance for loan losses:
Beginning balance	0	0	0	0
Provision for loan losses	0	0	0	0
Recoveries	0	0	0	0
Charge-offs	0	0	0	0
Ending balance	$ 0	$ 0	$ 0	$ 0

Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

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Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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Amount of expense related to estimated loss from loan and lease transactions.

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