v3.10.0.1
Document and Entity Information - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Feb. 15, 2019
Jun. 30, 2018
Document And Entity Information [Abstract]      
Entity Registrant Name Spark Therapeutics, Inc.    
Entity Central Index Key 0001609351    
Current Fiscal Year End Date --12-31    
Entity Filer Category Large Accelerated Filer    
Entity Emerging Growth Company false    
Entity Small Business false    
Entity Shell Company false    
Document Type 10-K    
Trading Symbol ONCE    
Document Period End Date Dec. 31, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Common Stock, Shares Outstanding   37,961,302  
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 2,583.3