| Cover | Feb. 16, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 16, 2021 |
| Entity File Number | 0-20713 |
| Entity Registrant Name | CASI PHARMACEUTICALS, INC. |
| Entity Central Index Key | 0000895051 |
| Entity Tax Identification Number | 58-1959440 |
| Entity Incorporation, State or Country Code | DE |
| Entity Address, Address Line One | 9620 Medical Center Drive |
| Entity Address, Address Line Two | Suite 300 |
| Entity Address, City or Town | Rockville |
| Entity Address, State or Province | MD |
| Entity Address, Postal Zip Code | 20850 |
| City Area Code | 240 |
| Local Phone Number | 864-2600 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | CASI |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
