Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2024	Oct. 29, 2024
Document Information [Line Items]
Entity Central Index Key	0000903419
Entity Registrant Name	ALERUS FINANCIAL CORP
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2024
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
Document Transition Report	false
Entity File Number	001-39036
Entity Incorporation, State or Country Code	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 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
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		25,338,280