Loans and Allowance for Loan Losses - Troubled Debt Restructurings That Are Performing (Details) $ in Thousands	12 Months Ended
Dec. 31, 2020 USD ($) contract	Dec. 31, 2019 USD ($)	Dec. 31, 2018
Number	2	3	1
Performing Financial Instruments [Member]
Number	25	24
Amortized Cost	$ 15,911
Recorded investment		$ 6,494
Multi-Family Residential [Member] \| Performing Financial Instruments [Member]
Number	6	7
Amortized Cost	$ 1,700
Recorded investment		$ 1,873
Commercial Real Estate
Number	1
Commercial Real Estate \| Performing Financial Instruments [Member]
Number \| contract	1
Amortized Cost	$ 7,702
One-To-Four Family - Mixed Used Property [Member]
Number	1
One-To-Four Family - Mixed Used Property [Member] \| Performing Financial Instruments [Member]
Number	5	4
Amortized Cost	$ 1,731
Recorded investment		$ 1,481
One-To-Four Family - Residential [Member] \| Performing Financial Instruments [Member]
Number	3	3
Amortized Cost	$ 507
Recorded investment		$ 531
Taxi Medallion Portfolio Segment [Member] \| Performing Financial Instruments [Member]
Number	2	7
Amortized Cost	$ 440
Recorded investment		$ 1,668
Commercial Business and Other [Member] \| Performing Financial Instruments [Member]
Number	8	3
Amortized Cost	$ 3,831
Recorded investment		$ 941

The amount of amortized cost of financing receivables modified as troubled debt restructuring.

No definition available.

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

- Definition

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

+ References

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable modified as troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18845-111554

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=ffic_MultiFamilyResidentialMember
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_FinancingReceivablePortfolioSegmentAxis=ffic_OneToFourFamilyMixedUsedPropertyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=ffic_OneToFourFamilyResidentialMember
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_FinancingReceivablePortfolioSegmentAxis=ffic_CommercialBusinessAndOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: