Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2020	Apr. 30, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Mar. 31, 2020
Entity File Number	001-32964
Entity Registrant Name	THE FIRST OF LONG ISLAND CORPORATION
Entity Incorporation, State or Country Code	NY
Entity Tax Identification Number	11-2672906
Entity Address, Address Line One	10 Glen Head Road
Entity Address, City or Town	Glen Head
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	11545
City Area Code	516
Local Phone Number	671-4900
Title of 12(b) Security	Common stock, $0.10 par value per share
Trading Symbol	FLIC
Security Exchange Name	NASDAQ
Entity Central Index Key	0000740663
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding (in shares)		23,845,582