Document and Entity Information - shares
3 Months Ended
Mar. 31, 2019
May 03, 2019
Document and Entity Information    
Entity Registrant Name Assertio Therapeutics, Inc.  
Entity Central Index Key 0001005201  
Document Type 10-Q  
Document Period End Date Mar. 31, 2019  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding (in shares)   64,405,162
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q1  
Entity Smaller Reporting Company false  
Entity Emerging Growth Company false