Document and Entity Information - shares
3 Months Ended
Mar. 31, 2016
May. 12, 2016
Document and Entity Information [Abstract]    
Entity Registrant Name AveXis, Inc.  
Entity Central Index Key 0001652923  
Document Type 10-Q  
Document Period End Date Mar. 31, 2016  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   23,013,838
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q1