Loans Receivable and Allowance for Loan Losses - Loans Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 5,169,476	$ 4,962,289
Net deferred loan costs, fees and purchased premiums and discounts	16,621	16,893
Loans receivable	5,186,097	4,979,182
Real estate loans \| One-to-four family
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	1,844,507	1,830,186
Real estate loans \| Multifamily and commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	2,316,922	2,142,154
Real estate loans \| Construction
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	268,522	261,473
Commercial business loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	375,412	333,876
Consumer loans \| Home equity loans and advances
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	362,432	393,492
Consumer loans \| Other consumer loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total gross loans	$ 1,681	$ 1,108

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- Definition

Amount, before allowance and fees, of loans and leases receivable. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

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Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

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