| Document And Entity Information | Dec. 11, 2024 |
| Document Information [Line Items] | |
| Entity, Registrant Name | Alerus Financial Corporation |
| Document, Type | 8-K |
| Document, Period End Date | Dec. 11, 2024 |
| Entity, Incorporation, State or Country Code | DE |
| Entity, File Number | 001-39036 |
| Entity, Tax Identification Number | 45-0375407 |
| Entity, Address, Address Line One | 401 Demers Avenue |
| Entity, Address, City or Town | Grand Forks |
| Entity, Address, State or Province | ND |
| Entity, Address, Postal Zip Code | 58201 |
| City Area Code | 701 |
| Local Phone Number | 795-3200 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $1.00 par value per share |
| Trading Symbol | ALRS |
| Security Exchange Name | NASDAQ |
| Entity, Emerging Growth Company | true |
| Entity, Ex Transition Period | false |
| Amendment Flag | false |
| Entity, Central Index Key | 0000903419 |
