| Cover | Jan. 21, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 21, 2021 |
| Entity Registrant Name | Investar Holding Corp |
| Entity Incorporation, State or Country Code | LA |
| Entity File Number | 001-36522 |
| Entity Tax Identification Number | 27-1560715 |
| Entity Address, Address Line One | 10500 Coursey Blvd. |
| Entity Address, City or Town | Baton Rouge |
| Entity Address, State or Province | LA |
| Entity Address, Postal Zip Code | 70816 |
| City Area Code | 225 |
| Local Phone Number | 227-2222 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, $1.00 par value per share |
| Trading Symbol | ISTR |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001602658 |
| Amendment Flag | false |
