| Cover | Jan. 28, 2021 |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jan. 28, 2021 |
| Entity File Number | 0-13368 |
| Entity Registrant Name | FIRST MID BANCSHARES, INC. |
| Entity Central Index Key | 0000700565 |
| Entity Tax Identification Number | 37-1103704 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 1421 Charleston Avenue |
| Entity Address, City or Town | Mattoon |
| Entity Address, State or Province | IL |
| Entity Address, Postal Zip Code | 61938 |
| City Area Code | 217 |
| Local Phone Number | 234-7454 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | FMBH |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
