| Document and Entity Information | Dec. 17, 2019 |
| Cover [Abstract] | |
| Current Fiscal Year End Date | --12-31 |
| Amendment Flag | false |
| Entity Central Index Key | 0001609351 |
| Document Type | 8-K |
| Document Period End Date | Dec. 17, 2019 |
| Entity Registrant Name | Spark Therapeutics, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-36819 |
| Entity Tax Identification Number | 46-2654405 |
| Entity Address, Address Line One | 3737 Market Street |
| Entity Address, Address Line Two | Suite 1300 |
| Entity Address, City or Town | Philadelphia |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 19104 |
| City Area Code | 888 |
| Local Phone Number | 772-7560 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.001 par value per share |
| Trading Symbol | ONCE |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
