Document and Entity Information - shares
6 Months Ended
Jun. 30, 2018
Jul. 27, 2018
Document and Entity Information    
Entity Registrant Name Adamas Pharmaceuticals Inc  
Entity Central Index Key 0001328143  
Document Type 10-Q  
Document Period End Date Jun. 30, 2018  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Accelerated Filer  
Entity Common Stock, Shares Outstanding (in shares)   27,190,453
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2