Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Oct. 31, 2021
Cover [Abstract]
Entity Central Index Key	0000923139
Entity Registrant Name	Flushing Financial Corporation
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2021
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Sep. 30, 2021
Entity File Number	001-33013
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	11-3209278
Entity Address, Address Line One	220 RXR Plaza
Entity Address, City or Town	Uniondale
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	11556
City Area Code	(718)
Local Phone Number	961-5400
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	FFIC
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		30,676,195