Loans Receivable and Allowance for Loan Losses - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Allowance for loan losses:
Beginning balance	$ 62,403	$ 62,524	$ 62,342	$ 58,178
Provision for loan losses	1,157	1,500	1,705	5,900
Recoveries	35	149	434	518
Charge-offs	(966)	(767)	(1,852)	(1,190)
Ending balance	62,629	63,406	62,629	63,406
Real estate loans \| One-to-four family
Allowance for loan losses:
Beginning balance	15,610	18,549	15,232	19,991
Provision for loan losses	347	(809)	1,215	(2,362)
Recoveries	4	108	29	280
Charge-offs	(228)	(323)	(743)	(384)
Ending balance	15,733	17,525	15,733	17,525
Real estate loans \| Multifamily and commercial
Allowance for loan losses:
Beginning balance	22,679	22,802	23,251	19,933
Provision for loan losses	290	965	(282)	3,962
Recoveries	0	0	0	0
Charge-offs	0	0	0	(128)
Ending balance	22,969	23,767	22,969	23,767
Real estate loans \| Construction
Allowance for loan losses:
Beginning balance	8,806	6,728	7,217	5,217
Provision for loan losses	(1,047)	420	541	1,928
Recoveries	1	0	2	3
Charge-offs	0	0	0	0
Ending balance	7,760	7,148	7,760	7,148
Commercial business loans
Allowance for loan losses:
Beginning balance	12,718	10,920	14,176	8,275
Provision for loan losses	2,040	1,118	485	3,902
Recoveries	8	24	374	111
Charge-offs	(738)	(197)	(1,007)	(423)
Ending balance	14,028	11,865	14,028	11,865
Consumer loans \| Home equity loans and advances
Allowance for loan losses:
Beginning balance	2,583	2,870	2,458	4,577
Provision for loan losses	(474)	202	(255)	(1,607)
Recoveries	22	17	29	119
Charge-offs	0	(246)	(101)	(246)
Ending balance	2,131	2,843	2,131	2,843
Consumer loans \| Other consumer loans
Allowance for loan losses:
Beginning balance	7	7	8	8
Provision for loan losses	1	1	1	3
Recoveries	0	0	0	5
Charge-offs	0	(1)	(1)	(9)
Ending balance	8	7	8	7
Unallocated
Allowance for loan losses:
Beginning balance	0	648	0	177
Provision for loan losses	0	(397)	0	74
Recoveries	0	0	0	0
Charge-offs	0	0	0	0
Ending balance	$ 0	$ 251	$ 0	$ 251

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

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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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