Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Feb. 29, 2024	Jun. 30, 2023
Document and Entity Information
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Document Transition Report	false
Entity File Number	001-39036
Entity Registrant Name	ALERUS FINANCIAL CORPORATION
Entity Incorporation, State	DE
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
Title of 12(b) Security	Common Stock, par value $1.00 per share
Trading Symbol	ALRS
Security Exchange Name	NASDAQ
Entity Well Known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding			19,737,829
Entity Public Float				$ 341,868,115
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Central Index Key	0000903419
Amendment Flag	false
Auditor Name	RSM US LLP	CliftonLarsonAllen LLP
Auditor Firm ID	49	655
Auditor Location	Des Moines, Iowa	Minneapolis, Minnesota