Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 31, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Trading Symbol CASA  
Entity Registrant Name Casa Systems Inc  
Entity Central Index Key 0001333835  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Accelerated Filer  
Entity Shell Company false  
Entity Small Business false  
Entity Emerging Growth Company true  
Entity Ex Transition Period false  
Entity File Number 001-38324  
Entity Tax Identification Number 753108867  
Entity Address, Address Line One 100 Old River Road  
Entity Address, City or Town Andover  
Entity Address, State or Province Massachusetts  
Entity Address, Postal Zip Code 01810  
City Area Code 978  
Local Phone Number 688-6706  
Entity Common Stock, Shares Outstanding   84,030,902