Document and Entity Information - USD ($)	12 Months Ended
	Jan. 31, 2022	Apr. 11, 2022	Jul. 31, 2021
Document And Entity Information
Document Type	10-K
Document Annual Report	true
Document Period End Date	Jan. 31, 2022
Document Transition Report	false
Entity File Number	001-31756
Entity Registrant Name	ARGAN INC
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
Title of 12(b) Security	Common Stock, $0.15 par value
Trading Symbol	AGX
Security Exchange Name	NYSE
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	false
Icfr Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 382,871,469
Entity Common Stock, Shares Outstanding		14,815,609
Auditor Name	GRANT THORNTON LLP
Auditor Firm ID	248
Auditor Location	Arlington, Virginia
Entity Central Index Key	0000100591
Document Fiscal Year Focus	2022
Current Fiscal Year End Date	--01-31
Document Fiscal Period Focus	FY
Amendment Flag	false