Borrowed Funds - Terms of the Securities Issued by the Trusts (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2016
Flushing Financial Capital Trust II [Member] \| Capital Securities [Member]
Issue Date	Jun. 20, 2007
Initial Rate	7.14%
First Reset Date	Sep. 01, 2012
Spread over 3-month LIBOR	1.41%
Maturity Date	Sep. 01, 2037
Flushing Financial Capital Trust III [Member] \| Capital Securities [Member]
Issue Date	Jun. 21, 2007
Initial Rate	6.89%
First Reset Date	Jun. 15, 2012
Spread over 3-month LIBOR	1.44%
Maturity Date	Sep. 15, 2037
Flushing Financial Capital Trust IV [Member] \| Capital Securities [Member]
Issue Date	Jul. 03, 2007
Initial Rate	6.85%
First Reset Date	Jul. 30, 2012
Spread over 3-month LIBOR	1.42%
Maturity Date	Jul. 30, 2037
Subordinated Debentures
Amount		$ 75,000
$75,000 subordinate debentures due December 15, 2026
Amount	$ 75,000
Issue Date	Dec. 12, 2016
Initial Rate	5.25%
First Reset Date	Dec. 15, 2021
First Call Date	Dec. 15, 2021
Maturity Date	Dec. 15, 2026
$75,000 subordinate debentures due December 15, 2026 \| London Interbank Offered Rate (LIBOR) [Member]
Spread over 3-month LIBOR	3.44%
$7,500 subordinate debentures due December 17, 2025
Amount	$ 7,500
Issue Date	Dec. 17, 2015
Initial Rate	7.38%
First Call Date	Dec. 20, 2020
Maturity Date	Dec. 17, 2025
$7,750 Subordinate debentures.
Amount	$ 7,750
Issue Date	Dec. 17, 2015
Initial Rate	6.50%
First Reset Date	Dec. 20, 2020
First Call Date	Dec. 20, 2020
Maturity Date	Dec. 17, 2025
$7,750 Subordinate debentures. \| London Interbank Offered Rate (LIBOR) [Member]
Spread over 3-month LIBOR	4.88%

First reset date for the interest rate on the debt instrument.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

Earliest date before maturity when the issuer can call the outstanding debt instrument for repayment or conversion to equity, in CCYY-MM-DD format.

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Face (par) amount of debt instrument at time of issuance.

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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- Definition

Date the debt instrument was issued, in CCYY-MM-DD format.

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- Definition

Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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