| Document and Entity Information Document | Feb. 27, 2020 |
| Cover page. | |
| Document Type | 8-K |
| Document Period End Date | Feb. 27, 2020 |
| Entity Registrant Name | OPORTUN FINANCIAL CORPORATION |
| Entity Central Index Key | 0001538716 |
| Amendment Flag | false |
| Entity File Number | 001-39050 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 45-3361983 |
| Entity Address, Address Line One | 2 Circle Star Way |
| Entity Address, City or Town | San Carlos, |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94070 |
| City Area Code | 650 |
| Local Phone Number | 810-8823 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.0001 par value per share |
| Trading Symbol | OPRT |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
