Loans - Risk category of our loan portfolio (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
2021	$ 587,016
2020	770,657
2019	944,135
2018	1,042,042
2017	749,913
Prior	2,352,825
Revolving Loans Amortized Cost Basis	253,614
Lines of credit converted to term loans	18,604
Total	6,718,806
One-To-Four Family - Residential Portfolio Segment [Member]
2021	57,316
2020	32,378
2019	36,977
2018	34,934
2017	24,480
Prior	82,128
Revolving Loans Amortized Cost Basis	10,874
Lines of credit converted to term loans	18,604
Total	297,691
One-To-Four Family - Residential Portfolio Segment [Member] \| Pass [Member]
2021	57,316
2020	31,897
2019	36,253
2018	32,818
2017	20,935
Prior	75,903
Revolving Loans Amortized Cost Basis	10,524
Lines of credit converted to term loans	15,288
Total	280,934
One-To-Four Family - Residential Portfolio Segment [Member] \| Watch [Member]
2020	481
2019	724
2018	280
2017	2,430
Prior	1,541
Revolving Loans Amortized Cost Basis	190
Lines of credit converted to term loans	2,287
Total	7,933
One-To-Four Family - Residential Portfolio Segment [Member] \| Special Mention [Member]
2017	1,115
Prior	517
Revolving Loans Amortized Cost Basis	160
Total	1,792
One-To-Four Family - Residential Portfolio Segment [Member] \| Substandard [Member]
2018	1,836
Prior	4,167
Lines of credit converted to term loans	1,029
Total	7,032
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member]
2021	18,221
2020	35,902
2019	71,259
2018	78,786
2017	61,128
Prior	320,453
Total	585,749
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Pass [Member]
2021	18,221
2020	35,902
2019	71,259
2018	75,193
2017	54,249
Prior	308,869
Total	563,693
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Watch [Member]
2018	3,092
2017	6,118
Prior	7,668
Total	16,878
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Special Mention [Member]
2017	761
Prior	1,438
Total	2,199
One-To-Four Family - Mixed-Use Property Portfolio Segment [Member] \| Substandard [Member]
2018	501
Prior	2,478
Total	2,979
Commercial Real Estate
2021	62,417
2020	172,367
2019	267,723
2018	278,932
2017	182,657
Prior	765,811
Total	1,729,907
Commercial Real Estate \| Pass [Member]
2021	58,238
2020	171,433
2019	256,707
2018	266,369
2017	180,000
Prior	680,308
Total	1,613,055
Commercial Real Estate \| Watch [Member]
2021	4,179
2020	934
2019	3,433
2018	5,708
2017	2,657
Prior	83,926
Total	100,837
Commercial Real Estate \| Special Mention [Member]
2018	6,855
Prior	1,542
Total	8,397
Commercial Real Estate \| Substandard [Member]
2019	7,583
Prior	35
Total	7,618
Construction Portfolio Segment [Member]
2021	3,079
2020	23,121
2019	16,912
2018	11,103
2017	8,496
Total	62,711
Construction Portfolio Segment [Member] \| Pass [Member]
2021	3,079
2020	23,121
2019	14,797
2018	1,960
Total	42,957
Construction Portfolio Segment [Member] \| Watch [Member]
2019	2,115
2018	8,284
2017	5,904
Total	16,303
Construction Portfolio Segment [Member] \| Special Mention [Member]
2018	859
2017	2,592
Total	3,451
Multi-family Residential Portfolio Segment [Member]
2021	168,396
2020	243,515
2019	345,571
2018	464,611
2017	361,911
Prior	952,810
Revolving Loans Amortized Cost Basis	6,945
Total	2,543,759
Multi-family Residential Portfolio Segment [Member] \| Pass [Member]
2021	168,396
2020	240,612
2019	340,195
2018	449,407
2017	360,108
Prior	941,236
Revolving Loans Amortized Cost Basis	6,346
Total	2,506,300
Multi-family Residential Portfolio Segment [Member] \| Watch [Member]
2020	2,111
2019	4,205
2018	12,605
Prior	10,834
Revolving Loans Amortized Cost Basis	398
Total	30,153
Multi-family Residential Portfolio Segment [Member] \| Special Mention [Member]
2020	792
2019	468
Total	1,260
Multi-family Residential Portfolio Segment [Member] \| Substandard [Member]
2019	703
2018	2,599
2017	1,803
Prior	740
Revolving Loans Amortized Cost Basis	201
Total	6,046
Commercial Business Secured By Portfolio Segment [member]
2021	96,311
2020	117,211
2019	90,838
2018	70,737
2017	40,152
Prior	151,307
Total	566,556
Commercial Business Secured By Portfolio Segment [member] \| Pass [Member]
2021	96,311
2020	93,588
2019	38,733
2018	52,180
2017	28,173
Prior	99,637
Total	408,622
Commercial Business Secured By Portfolio Segment [member] \| Watch [Member]
2020	23,623
2019	51,501
2018	18,557
2017	11,979
Prior	47,442
Total	153,102
Commercial Business Secured By Portfolio Segment [member] \| Special Mention [Member]
2019	604
Total	604
Commercial Business Secured By Portfolio Segment [member] \| Substandard [Member]
Prior	4,228
Total	4,228
Commercial Business Portfolio Segment [Member]
2021	51,021
2020	79,015
2019	113,502
2018	98,791
2017	67,357
Prior	76,382
Revolving Loans Amortized Cost Basis	235,716
Total	721,784
Commercial Business Portfolio Segment [Member] \| Pass [Member]
2021	51,015
2020	72,432
2019	90,417
2018	76,675
2017	29,154
Prior	73,507
Revolving Loans Amortized Cost Basis	207,786
Total	600,986
Commercial Business Portfolio Segment [Member] \| Watch [Member]
2021	6
2020	1,683
2019	22,505
2018	19,308
2017	33,143
Prior	43
Revolving Loans Amortized Cost Basis	22,493
Total	99,181
Commercial Business Portfolio Segment [Member] \| Special Mention [Member]
2019	45
2018	2,488
2017	103
Revolving Loans Amortized Cost Basis	3,207
Total	5,843
Commercial Business Portfolio Segment [Member] \| Substandard [Member]
2020	4,900
2019	535
2018	320
2017	4,957
Prior	1,903
Revolving Loans Amortized Cost Basis	995
Total	13,610
Commercial Business Portfolio Segment [Member] \| Doubtful [Member]
Prior	929
Revolving Loans Amortized Cost Basis	1,235
Total	2,164
Small Business Administration Portfolio Segment [Member]
2021	130,255
2020	67,148
2019	1,353
2018	4,148
2017	3,732
Prior	3,882
Total	210,518
Small Business Administration Portfolio Segment [Member] \| Pass [Member]
2021	130,255
2020	67,148
2019	1,292
2018	1,560
2017	654
Prior	2,920
Total	203,829
Small Business Administration Portfolio Segment [Member] \| Watch [Member]
2019	61
2018	2,588
2017	1,946
Prior	849
Total	5,444
Small Business Administration Portfolio Segment [Member] \| Special Mention [Member]
2017	140
Prior	107
Total	247
Small Business Administration Portfolio Segment [Member] \| Substandard [Member]
2017	992
Prior	6
Total	998
Other Portfolio Segment [Member]
Prior	52
Revolving Loans Amortized Cost Basis	79
Total	131
Other Portfolio Segment [Member] \| Pass [Member]
Prior	52
Revolving Loans Amortized Cost Basis	79
Total	131
Consumer Portfolio Segment [Member]
Mortgage Loans in Process of Foreclosure, Amount	$ 9,300	$ 5,900

The amount of financial receivables originated through conversion of line of credit in to term loans.

No definition available.

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

- Definition

Amount of financing receivable originated more than five years prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated four years prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated in current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated in fiscal year prior to current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919232-210447

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448

+ Details

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

- Definition

Amount of financing receivable originated three years prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable originated two years prior to current fiscal year.

+ References

+ Details

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

- Definition

Amount of financing receivable that can be withdrawn, repaid and redrawn.

+ References

+ Details

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

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL49126937-111524

+ Details

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

- Definition

Amount, before allowance for credit loss, of financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 79
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922352-210448

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919230-210447

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448

+ Details

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

- Details

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

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_PassMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=ffic_WatchMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_SpecialMentionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_SubstandardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_InternalCreditAssessmentAxis=us-gaap_DoubtfulMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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