Loans and Allowance for Loan Losses (Details) $ in Thousands	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Number of Contracts	0
Financing Receivable Modifications Amount Recovered	$ 100
Financing Receivable, Nonaccrual	12,813	$ 16,253
Total loans, net of fees and costs	5,772,206	$ 5,551,484
Servicing Mortgage Loans [Member]
Servicing Asset, Loans Serviced, Amount	32,500
Servicing SBA Loans [Member]
Servicing Asset, Loans Serviced, Amount	$ 15,800
Multi-family Residential Property and Commercial Real Estate and Commerical Business and Other Loans [Member]
Loan Origination, Underwriting Requirements, Minimum Debt Service Coverage	125.00%
Loan Origination, Value, Maximum Percentage	75.00%
Multi-family Residential Property and Commercial Real Estate and Commerical Business and Other Loans [Member] \| Gross Loans [Member] \| Credit Concentration Risk [Member]
Concentration Risk, Percentage	84.80%	84.70%
Commercial Real Estate Portfolio Segment [Member]
Number of Real Estate Classified as Troubled Debt Restructuring Sold		1
Financing Receivable, Modification, Sold During Period		$ 1,800
Loss on Sale of Real Estate Classified as Troubled Debt Restructuring		$ 300
Commercial Real Estate Portfolio Segment [Member] \| Nonperforming Financial Instruments [Member]
Financing Receivable Modifications Amount Transferred	$ 300
Taxi Medallion Portfolio Segment [Member]
Financing Receivable, Modifications, Number of Contracts, Paid Off	4	4
Financing Receivable, Modifications, Amount Paid Off	$ 900	$ 1,400
Number of Assets Foreclosed on During the Period		1
Total loans, net of fees and costs	1,100
Taxi Medallion Portfolio Segment [Member] \| Other Assets [Member]
Other Repossessed Assets		$ 100
Taxi Medallion Portfolio Segment [Member] \| Performing Financial Instruments [Member]
Financing Receivable, Nonaccrual	$ 1,700	$ 3,900
Commercial Business and Other Portfolio Segment [Member]
Number of Real Estate Classified as Troubled Debt Restructuring Sold	1
TDR Loans Transferred to Non-performing, Number of Contracts		1
Commercial Business and Other Portfolio Segment [Member] \| Performing Financial Instruments [Member]
Financing Receivable, Nonaccrual	$ 900

Represents the amount of modified TDR sold during the period.

No definition available.

Name:	ffic_FinancingReceivableModificationSoldDuringPeriod
Namespace Prefix:	ffic_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of financing receivables paid off that have been modified by troubled debt restructurings.

+ References

No definition available.

+ Details

Name:	ffic_FinancingReceivableModificationsAmountPaidOff
Namespace Prefix:	ffic_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of financing receivable recovered.

+ References

No definition available.

+ Details

Name:	ffic_FinancingReceivableModificationsAmountRecovered
Namespace Prefix:	ffic_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of financing receivable transferred.

+ References

No definition available.

+ Details

Name:	ffic_FinancingReceivableModificationsAmountTransferred
Namespace Prefix:	ffic_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of financing receivables paid off that have been modified by troubled debt restructurings.

+ References

No definition available.

+ Details

Name:	ffic_FinancingReceivableModificationsNumberOfContractsPaidOff
Namespace Prefix:	ffic_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum debt service coverage percentage required to meet the company's underwriting requirements for loan origination.

+ References

No definition available.

+ Details

Name:	ffic_LoanOriginationUnderwritingRequirementsMinimumDebtServiceCoverage
Namespace Prefix:	ffic_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum percentage of appraised value or purchase price of property of which the company will originate loans.

+ References

No definition available.

+ Details

Name:	ffic_LoanOriginationValueMaximumPercentage
Namespace Prefix:	ffic_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the amount of loss on sale of real estate classified as troubled debt restructuring (TDR).

+ References

No definition available.

+ Details

Name:	ffic_LossOnSaleOfRealEstateClassifiedAsTroubledDebtRestructuring
Namespace Prefix:	ffic_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents number of assets foreclosed on during the period.

+ References

No definition available.

+ Details

Name:	ffic_NumberOfAssetsForeclosedOnDuringThePeriod
Namespace Prefix:	ffic_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents number of real estate which is classified as troubled debt restructuring (TDR) sold during the period.

+ References

No definition available.

+ Details

Name:	ffic_NumberOfRealEstateClassifiedAsTroubledDebtRestructuringSold
Namespace Prefix:	ffic_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Aggregate amount of loans serviced for others as part of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

+ References

No definition available.

+ Details

Name:	ffic_ServicingAssetLoansServicedAmount
Namespace Prefix:	ffic_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Number of TDR loans transferred to non-performing loans during the period.

+ References

No definition available.

+ Details

Name:	ffic_TDRLoansTransferredToNonPerformingNumberOfContracts
Namespace Prefix:	ffic_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919258-210447

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

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

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of assets other than real property that were received in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5162-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4437-111522

+ Details

Name:	us-gaap_OtherForeclosedAssets
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancialInstrumentAxis=ffic_ServicingMortgageLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=ffic_ServicingSBALoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=ffic_MultiFamilyResidentialPropertyAndCommercialRealestateAndCommercialBusinessAndOtherLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=ffic_GrossLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CreditConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_NonperformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=ffic_TaxiMedallionPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_PerformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=ffic_CommercialBusinessAndOtherPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: