| Cover | Mar. 09, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 9, 2021 |
| Entity File Number | 001-38128 |
| Entity Registrant Name | Checkpoint Therapeutics, Inc. |
| Entity Central Index Key | 0001651407 |
| Entity Tax Identification Number | 47-2568632 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 2 Gansevoort Street |
| Entity Address, Address Line Two | 9th Floor |
| Entity Address, City or Town | New York |
| Entity Address, State or Province | NY |
| Entity Address, Postal Zip Code | 10014 |
| City Area Code | 781 |
| Local Phone Number | 652-4500 |
| 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 $0.0001 per share |
| Trading Symbol | CKPT |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
