| Document and Entity Information | Jan. 24, 2022 |
| Document and Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 24, 2022 |
| 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 |
| Entity Address, Adress Line Two | 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.15 Par Value |
| Trading Symbol | AGX |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000100591 |
| Amendment Flag | false |
