Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Mar. 01, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-39294
Entity Registrant Name	ASSERTIO HOLDINGS, INC.
Entity Central Index Key	0001808665
Amendment Flag	false
Document Fiscal Period Focus	FY
Document Fiscal Year Focus	2020
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	85-0598378
Entity Address, Address Line One	100 South Saunders Road
Entity Address, Address Line Two	Suite 300
Entity Address, City or Town	Lake Forest
Entity Address, State or Province	IL
Entity Address, Postal Zip Code	60045
City Area Code	224
Local Phone Number	419‑7106
Title of 12(b) Security	Common Stock, $0.0001 par value
Trading Symbol	ASRT
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	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 89.9
Entity Common Stock, Shares Outstanding		173,436,800
Documents Incorporated by Reference	Part III of this Annual Report on Form 10-K incorporates by reference portions of the registrant’s Proxy Statement for its 2021 Annual Meeting of Stockholders, which Proxy Statement will be filed with the United States Securities and Exchange Commission within 120 days after the end of the registrant’s 2020 fiscal year.