Securities - Amortized Cost and Fair Value of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Securities held-to-maturity, amortized cost	$ 74,811
Securities held-to-maturity, amortized cost	73,711	$ 57,868
Securities held-to-maturity, fair value	62,550	62,029
Securities held-to-maturity, gross Unrecognized gains		3,299
Securities held-to-maturity, gross Unrecognized losses	12,261
Securities held-to-maturity, allowance for credit losses	(1,100)	(862)	$ (907)
Securities available for sale, amortized cost, total other securities	826,881	786,425
Securities available for sale, fair value	735,357	777,236
Securities available for sale, gross unrealized gains	5	3,031
Securities available for sale, gross unrealized losses	91,529	12,220
Other Securities [Member]
Securities available for sale, amortized cost, total other securities	1,516	1,695
Securities available for sale, fair value	1,516	1,695
Securities available for sale, gross unrealized gains	0	0
Securities available for sale, gross unrealized losses	0	0
US Government Agencies Debt Securities [Member]
Securities available for sale, amortized cost, total other securities	83,720	5,599
Securities available for sale, fair value	81,103	5,590
Securities available for sale, gross unrealized gains	2	0
Securities available for sale, gross unrealized losses	2,619	9
Corporate Debt Securities [Member]
Securities available for sale, amortized cost, total other securities	146,430	107,423
Securities available for sale, fair value	131,766	104,370
Securities available for sale, gross unrealized gains	0	136
Securities available for sale, gross unrealized losses	14,664	3,189
US States and Political Subdivisions Debt Securities [Member]
Securities held-to-maturity, amortized cost	66,936	50,836
Securities held-to-maturity, fair value	55,561	53,362
Securities held-to-maturity, gross Unrecognized gains		2,526
Securities held-to-maturity, gross Unrecognized losses	11,375
Mutual Fund Debt Securities [Member]
Securities available for sale, amortized cost, total other securities	11,211	12,485
Securities available for sale, fair value	11,211	12,485
Securities available for sale, gross unrealized gains	0	0
Securities available for sale, gross unrealized losses	0	0
Collateralized Debt Obligations [Member]
Securities available for sale, amortized cost, total other securities	129,684	81,166
Securities available for sale, fair value	125,478	80,912
Securities available for sale, gross unrealized gains	0	1
Securities available for sale, gross unrealized losses	4,206	255
Other Debt Obligations
Securities held-to-maturity, amortized cost	66,936	50,836
Securities held-to-maturity, amortized cost	65,836	49,974
Securities held-to-maturity, fair value	55,561	53,362
Securities held-to-maturity, gross Unrecognized gains		2,526
Securities held-to-maturity, gross Unrecognized losses	11,375
Securities held-to-maturity, allowance for credit losses	(1,100)	(862)
Securities available for sale, fair value	351,074	205,052
Collateralized Mortgage Backed Securities
Securities held-to-maturity, amortized cost	7,875	7,894
Securities held-to-maturity, amortized cost	7,875	7,894
Securities held-to-maturity, fair value	6,989	8,667
Securities held-to-maturity, gross Unrecognized gains		773
Securities held-to-maturity, gross Unrecognized losses	886
Securities available for sale, amortized cost, total other securities	454,320	578,057
Securities available for sale, fair value	384,283	572,184
Securities available for sale, gross unrealized gains	3	2,894
Securities available for sale, gross unrealized losses	70,040	8,767
REMIC and CMO [Member]
Securities available for sale, amortized cost, total other securities	175,712	210,948
Securities available for sale, fair value	148,414	208,509
Securities available for sale, gross unrealized gains	0	1,217
Securities available for sale, gross unrealized losses	27,298	3,656
GNMA [Member]
Securities available for sale, amortized cost, total other securities	9,193	10,572
Securities available for sale, fair value	7,317	10,286
Securities available for sale, gross unrealized gains	3	30
Securities available for sale, gross unrealized losses	1,879	316
FNMA [Member]
Securities held-to-maturity, amortized cost	7,875	7,894
Securities held-to-maturity, fair value	6,989	8,667
Securities held-to-maturity, gross Unrecognized gains		773
Securities held-to-maturity, gross Unrecognized losses	886
Securities available for sale, amortized cost, total other securities	172,690	203,777
Securities available for sale, fair value	148,265	202,938
Securities available for sale, gross unrealized gains	0	1,321
Securities available for sale, gross unrealized losses	24,425	2,160
FHLMC [Member]
Securities available for sale, amortized cost, total other securities	96,725	152,760
Securities available for sale, fair value	80,287	150,451
Securities available for sale, gross unrealized gains	0	326
Securities available for sale, gross unrealized losses	16,438	2,635
Available for Sale Securities Excluding Mortgage Backed Securities [Member]
Securities available for sale, amortized cost, total other securities	372,561	208,368
Securities available for sale, fair value	351,074	205,052
Securities available for sale, gross unrealized gains	2	137
Securities available for sale, gross unrealized losses	$ 21,489	$ 3,453

Amount of investment in debt security measured at amortized cost, before allowance for credit losses.

No definition available.

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

- Definition

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).

+ 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 (b)
-URI https://asc.fasb.org/extlink&oid=126970911&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 https://asc.fasb.org/extlink&oid=126970911&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 https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

+ 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 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 4: 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 https://asc.fasb.org/extlink&oid=126970911&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 allowance for credit loss for 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 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aaa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

+ Details

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

- Definition

Amount, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI https://asc.fasb.org/extlink&oid=124255953&loc=SL82919253-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI https://asc.fasb.org/extlink&oid=123577603&loc=SL6953401-111524

Reference 4: 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 https://asc.fasb.org/extlink&oid=126970911&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

+ 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

+ 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 https://asc.fasb.org/extlink&oid=126970911&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=SL120269820-111563

+ Details

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

- Details

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

- Details

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

- 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=ffic_MutualFundDebtSecuritiesMember
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_OtherDebtSecuritiesMember
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_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_FNMAMember
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:

- Details

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