| Document and Entity Information - USD ($) $ in Millions | 12 Months Ended | ||
| Dec. 31, 2023 | Apr. 26, 2024 | Jun. 30, 2023 | |
| Cover [Abstract] | |||
| Document Type | 10-K/A | ||
| Amendment Flag | false | ||
| Document Annual Report | true | ||
| Document Period End Date | Dec. 31, 2023 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Document Fiscal Year Focus | 2023 | ||
| Document Fiscal Period Focus | FY | ||
| Document Transition Report | false | ||
| Entity File Number | 000-22245 | ||
| Entity Registrant Name | SEELOS THERAPEUTICS, INC. | ||
| Entity Central Index Key | 0001017491 | ||
| Entity Incorporation, State or Country Code | NV | ||
| Entity Tax Identification Number | 87-0449967 | ||
| 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 | ||
| Title of 12(b) Security | Common Stock, par value $0.001 per share | ||
| Trading Symbol | SEEL | ||
| Security Exchange Name | NASDAQ | ||
| Entity Well-known Seasoned Issuer | No | ||
| Entity Voluntary Filers | No | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Filer Category | Non-accelerated Filer | ||
| Entity Small Business | true | ||
| Entity Emerging Growth Company | false | ||
| ICFR Auditor Attestation Flag | false | ||
| Document Financial Statement Error Correction [Flag] | false | ||
| Entity Shell Company | false | ||
| Entity Public Float | $ 144.9 | ||
| Entity Common Stock, Shares Outstanding | 16,609,128 | ||
| Auditor Firm ID | 185 | ||
| Auditor Name | KPMG LLP | ||
| Auditor Location | Short Hills, NJ |
