| Cover | Oct. 16, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 16, 2020 |
| Entity File Number | 001-38487 |
| Entity Registrant Name | ORIGIN BANCORP, INC. |
| Entity Central Index Key | 0001516912 |
| Entity Tax Identification Number | 72-1192928 |
| Entity Incorporation, State or Country Code | LA |
| Entity Address, Address Line One | 500 South Service Road East |
| Entity Address, City or Town | Ruston |
| Entity Address, State or Province | LA |
| Entity Address, Postal Zip Code | 71270 |
| City Area Code | (318) |
| Local Phone Number | 255-2222 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $5.00 per share |
| Trading Symbol | OBNK |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Information, Former Legal or Registered Name | Not Applicable |
