v3.7.0.1
Document and Entity Information - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Mar. 03, 2017
Jun. 30, 2016
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2016    
Document Fiscal Year Focus 2016    
Document Fiscal Period Focus FY    
Trading Symbol RGNX    
Entity Registrant Name REGENXBIO Inc.    
Entity Central Index Key 0001590877    
Current Fiscal Year End Date --12-31    
Entity Filer Category Accelerated Filer    
Entity Well-known Seasoned Issuer No    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Common Stock, Shares Outstanding   26,513,335  
Entity Public Float     $ 169.9