Document and Entity Information - shares	9 Months Ended
	Oct. 31, 2020	Dec. 07, 2020
Document And Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Oct. 31, 2020
Document Transition Report	false
Entity File Number	001-31756
Entity Registrant Name	ARGAN INC
Entity Central Index Key	0000100591
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-1947195
Entity Address, Address Line One	One Church Street, Suite 201
Entity Address, City or Town	Rockville
Entity Address, State or Province	MD
Entity Address, Postal Zip Code	20850
City Area Code	301
Local Phone Number	315-0027
Amendment Flag	false
Current Fiscal Year End Date	--01-31
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Title of 12(b) Security	Common Stock, $.15 par value
Trading Symbol	AGX
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		15,689,969
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3