| Cover | Nov. 24, 2021 | Jun. 14, 2021 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Amendment Flag | false | |
| Document Period End Date | Nov. 24, 2021 | |
| Entity File Number | 000-22245 | |
| Entity Registrant Name | Seelos Therapeutics, Inc. | |
| Entity Central Index Key | 0001017491 | |
| Entity Tax Identification Number | 87-0449967 | |
| Entity Incorporation, State or Country Code | NV | |
| Entity Address, Address Line One | 300 Park Avenue | |
| Entity Address, Address Line Two | 2nd Floor | |
| Entity Address, City or Town | New York | |
| Entity Address, State or Province | NY | |
| Entity Address, Postal Zip Code | 10022 | |
| City Area Code | (646) | |
| Local Phone Number | 293-2100 | |
| Written Communications | false | |
| Soliciting Material | false | |
| Pre-commencement Tender Offer | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Title of 12(b) Security | Common Stock, $0.001 par value | |
| Trading Symbol | SEEL | |
| Security Exchange Name | NASDAQ | |
| Entity Emerging Growth Company | false |
