| Cover | Jul. 29, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 29, 2021 |
| Entity File Number | 001-11486 |
| Entity Registrant Name | ConnectOne Bancorp, Inc. |
| Entity Central Index Key | 0000712771 |
| Entity Tax Identification Number | 52-1273725 |
| Entity Incorporation, State or Country Code | NJ |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock |
| Trading Symbol | CNOB |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
