| Document and Entity Information | Jan. 28, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K/A |
| Amendment Flag | true |
| Amendment Description | The foregoing description of the Agreement is qualified in its entirety by reference to the full text of the Agreement, which is attached hereto as Exhibit 99.1 to this Current Report on Form 8-K/A and is incorporated herein by reference. |
| Document Period End Date | Jan. 28, 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 |
