Deposits (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Time Deposits, at or Above FDIC Insurance Limit	$ 497,400	$ 377,400
Interest-bearing Domestic Deposit, Brokered	1,102,000	856,300
Reciprocal Deposits	760,300	659,500
Deposits, Total	6,815,261	6,485,342
Letter of Credit Pledged as Collateral [Member]
Deposit Liabilities, Collateral Issued, Financial Instruments	1,118,700	1,073,700
Government Deposits [Member]
Deposits, Total	1,587,900	1,653,300
Government Deposits [Member] \| IntraFi Network deposits [Member]
Deposits, Total	642,600	604,800
Government Deposits [Member] \| Collateralized Deposits [Member]
Deposits, Total	945,300	1,048,500
Government Deposits [Member] \| Debt Securities Pledged as Collateral [Member]
Deposit Liabilities, Collateral Issued, Financial Instruments	177,000	155,700
Government Deposits [Member] \| Letter of Credit Pledged as Collateral [Member]
Deposit Liabilities, Collateral Issued, Financial Instruments	$ 1,118,700	$ 1,073,700

Represents the amount of reciprocal deposits.

No definition available.

Name:	ffic_ReciprocalDeposits
Namespace Prefix:	ffic_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of securities, mortgage loans, or other financial instruments pledged as collateral for deposits.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 50
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481047/942-405-50-1

+ Details

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

- Definition

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

Name:	us-gaap_Deposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of interest-bearing domestic third-party deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities.

+ References

+ Details

Name:	us-gaap_InterestBearingDomesticDepositBrokered
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of time deposit liabilities, including certificates of deposit, in denominations that meet or exceed the Federal Deposit Insurance Corporation (FDIC) insurance limit.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-SubTopic 405
-Topic 942
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481047/942-405-50-1

+ Details

Name:	us-gaap_TimeDepositsAtOrAboveFDICInsuranceLimit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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

- Details

Name:	us-gaap_FairValueByLiabilityClassAxis=ffic_GovernmentDepositsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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