| Document and Entity Information | Nov. 12, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Nov. 12, 2020 |
| Entity Registrant Name | ORCHARD THERAPEUTICS PLC |
| Entity Central Index Key | 0001748907 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-38722 |
| Entity Incorporation, State or Country Code | X0 |
| Entity Address, Address Line One | 108 Cannon Street |
| Entity Address, City or Town | London |
| Entity Address, Country | GB |
| Entity Address, Postal Zip Code | EC4N 6EU |
| City Area Code | 44 |
| Local Phone Number | (0) 203 808 8286 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Tax Identification Number | 00-0000000 |
| Title of 12(b) Security | American Depositary Shares, each representing one ordinary share, nominal value £0.10 per share |
| Trading Symbol | ORTX |
| Security Exchange Name | NASDAQ |
