Note 4 - Securities - Amortized Cost and Fair Value of Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Securities held-to-maturity, amortized cost	$ 31,093	$ 30,886
Securities held-to-maturity, fair value	28,654	29,699
Securities held-to-maturity, gross unrealized gains		0
Securities held-to-maturity, gross unrealized losses	2,439	1,187
Securities available for sale, amortized cost	752,716	748,350
Securities available for sale, fair value	728,623	738,354
Securities available for sale, gross unrealized gains	1,260	2,587
Securities available for sale, gross unrealized losses	25,353	12,583
Corporate Debt Securities [Member]
Securities available for sale, amortized cost	110,000	110,000
Securities available for sale, fair value	100,532	102,767
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses	9,468	7,233
US States and Political Subdivisions Debt Securities [Member]
Securities held-to-maturity, amortized cost	23,130	22,913
Securities held-to-maturity, fair value	21,281	21,889
Securities held-to-maturity, gross unrealized gains		0
Securities held-to-maturity, gross unrealized losses	1,849	1,024
Securities available for sale, amortized cost	100,576	101,680
Securities available for sale, fair value	101,608	103,199
Securities available for sale, gross unrealized gains	1,063	1,519
Securities available for sale, gross unrealized losses	31
Other Debt Obligations [Member]
Securities held-to-maturity, amortized cost	23,130	22,913
Securities held-to-maturity, fair value	21,281	21,889
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	1,849	1,024
Securities available for sale, fair value	214,755	228,704
Mutual Fund Debt Securities [Member]
Securities available for sale, amortized cost	11,427	11,575
Securities available for sale, fair value	11,427	11,575
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses
FNMA [Member]
Securities held-to-maturity, amortized cost	7,963	7,973
Securities held-to-maturity, fair value	7,373	7,810
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	590	163
Securities available for sale, amortized cost	133,359	136,198
Securities available for sale, fair value	129,222	135,474
Securities available for sale, gross unrealized gains	54	330
Securities available for sale, gross unrealized losses	4,191	1,054
Other Securities [Member]
Securities available for sale, amortized cost	1,188	1,110
Securities available for sale, fair value	1,188	1,110
Securities available for sale, gross unrealized gains
Securities available for sale, gross unrealized losses
Collateralized Debt Obligations [Member]
Securities available for sale, amortized cost		10,000
Securities available for sale, fair value		10,053
Securities available for sale, gross unrealized gains		53
Securities available for sale, gross unrealized losses
Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity, amortized cost	7,963	7,973
Securities held-to-maturity, fair value	7,373	7,810
Securities held-to-maturity, gross unrealized gains
Securities held-to-maturity, gross unrealized losses	590	163
Securities available for sale, amortized cost	529,525	513,985
Securities available for sale, fair value	513,868	509,650
Securities available for sale, gross unrealized gains	197	1,015
Securities available for sale, gross unrealized losses	15,854	5,350
Available for Sale Securities Excluding Mortgage Backed Securities [Member]
Securities available for sale, amortized cost	223,191	234,365
Securities available for sale, fair value	214,755	228,704
Securities available for sale, gross unrealized gains	1,063	1,572
Securities available for sale, gross unrealized losses	9,499	7,233
REMIC and CMO [Member]
Securities available for sale, amortized cost	342,394	328,668
Securities available for sale, fair value	332,381	325,302
Securities available for sale, gross unrealized gains	80	595
Securities available for sale, gross unrealized losses	10,093	3,961
GNMA [Member]
Securities available for sale, amortized cost	847	1,016
Securities available for sale, fair value	898	1,088
Securities available for sale, gross unrealized gains	51	72
Securities available for sale, gross unrealized losses
FHLMC [Member]
Securities available for sale, amortized cost	52,925	48,103
Securities available for sale, fair value	51,367	47,786
Securities available for sale, gross unrealized gains	12	18
Securities available for sale, gross unrealized losses	$ 1,570	$ 335

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

+ Details

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

- Definition

Amount of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109979856&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

+ Details

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

- Definition

Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

+ Details

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

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

+ Details

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

- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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