Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Mar. 14, 2019	Jun. 30, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Seelos Therapeutics, Inc.
Trading Symbol	SEEL
Entity Central Index Key	0001017491
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Is Entity's Reporting Status Current?	Yes
Entity Voluntary Filers	No
Entity Well-known Seasoned Issuer	No
Entity Shell Company	false
Entity Public Float			$ 9.1
Entity Common Stock, Shares Outstanding		18,406,019