Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 01, 2021	Jun. 30, 2020
Document and Entity Information [Abstract]
Document Type	10-K
Entity Central Index Key	0000712771
Document Period End Date	Dec. 31, 2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Document Fiscal Year Focus	2020
Current Fiscal Year End Date	--12-31
Document Annual Report	true
Document Transition Report	false
Entity File Number	000-11486
Entity Registrant Name	ConnectOne Bancorp, Inc.
Entity Incorporation, State or Country Code	NJ
Entity Tax Identification Number	52-1273725
Entity Address, Address Line One	301 Sylvan Avenue
Entity Address, City or Town	Englewood Cliffs
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	07632
City Area Code	201
Local Phone Number	816-8900
Title of 12(b) Security	Common Stock, no par value
Trading Symbol	CNOB
Name of Exchange on which Security is Registered	NASDAQ
Entity Well-Known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 593.2
Entity Common Stock, Shares Outstanding		39,785,398
Documents Incorporated By Reference Text Block	Definitive proxy statement in connection with the 2021 Annual Stockholders Meeting to be filed with the Commission pursuant to Regulation 14A will be incorporated by reference in Part III