| Document and Entity Information | Apr. 22, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Apr. 22, 2021 |
| Entity Registrant Name | OP BANCORP |
| Entity Central Index Key | 0001722010 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | true |
| Entity File Number | 001-38437 |
| Entity Incorporation, State or Country Code | CA |
| Entity Tax Identification Number | 81-3114676 |
| Entity Address, Address Line One | 1000 Wilshire Blvd |
| Entity Address, Address Line Two | Suite 500 |
| Entity Address, City or Town | Los Angeles |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 90017 |
| City Area Code | 213 |
| Local Phone Number | 892-9999 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, no par value |
| Trading Symbol | OPBK |
| Security Exchange Name | NASDAQ |
