Loans Receivable and Allowance for Loan Losses - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Allowance for loan losses:
Beginning balance	$ 62,342	$ 58,178
Provision for loan losses	436	2,000
Recoveries	341	181
Charge-offs	(348)	(407)
Ending balance	62,771	59,952
Real estate loans \| One-to-four family
Allowance for loan losses:
Beginning balance	15,232	19,991
Provision for loan losses	2,122	(1,229)
Recoveries	21	120
Charge-offs	0	(54)
Ending balance	17,375	18,828
Real estate loans \| Multifamily and commercial
Allowance for loan losses:
Beginning balance	23,251	19,933
Provision for loan losses	(2,265)	(707)
Recoveries	0	0
Charge-offs	0	(129)
Ending balance	20,986	19,097
Real estate loans \| Construction
Allowance for loan losses:
Beginning balance	7,217	5,217
Provision for loan losses	1,816	1,354
Recoveries	0	3
Charge-offs	0	0
Ending balance	9,033	6,574
Commercial business loans
Allowance for loan losses:
Beginning balance	14,176	8,275
Provision for loan losses	(1,996)	2,697
Recoveries	313	52
Charge-offs	(268)	(224)
Ending balance	12,225	10,800
Consumer loans \| Home equity loans and advances
Allowance for loan losses:
Beginning balance	2,458	4,576
Provision for loan losses	761	(657)
Recoveries	7	5
Charge-offs	(80)	0
Ending balance	3,146	3,924
Consumer loans \| Other consumer loans
Allowance for loan losses:
Beginning balance	8	8
Provision for loan losses	(2)	(2)
Recoveries	0	1
Charge-offs	0	0
Ending balance	6	7
Unallocated
Allowance for loan losses:
Beginning balance	0	178
Provision for loan losses	0	544
Recoveries	0	0
Charge-offs	0	0
Ending balance	$ 0	$ 722

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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- Definition

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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