| Document and Entity Information Document | Jan. 11, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 11, 2021 |
| Entity Registrant Name | NovoCure Limited |
| Entity Central Index Key | 0001645113 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | Y9 |
| Entity File Number | 001-37565 |
| Entity Tax Identification Number | 98-1057807 |
| Entity Address, Address Line One | No. 4 The Forum, Grenville Street |
| Entity Address, City or Town | St. Helier |
| Entity Address, Country | JE |
| Entity Address, Postal Zip Code | JE2 4UF |
| City Area Code | 44 (0) 15 |
| Local Phone Number | 3475 6700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Ordinary Shares, no par value |
| Trading Symbol | NVCR |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
