Cover - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Mar. 01, 2022
Jun. 30, 2021
Cover [Abstract]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2021    
Current Fiscal Year End Date --12-31    
Document Transition Report false    
Entity File Number 001-39294    
Entity Registrant Name ASSERTIO HOLDINGS, INC.    
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     $ 68.4
Entity Common Stock, Shares Outstanding   45,331,803  
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 2021 fiscal year.    
Entity Central Index Key 0001808665    
Amendment Flag false    
Document Fiscal Period Focus FY    
Document Fiscal Year Focus 2021