| Document and Entity Information Document | Jan. 11, 2021 | Apr. 30, 2021 |
| Cover [Abstract] | ||
| Document Type | 8-K | |
| Document Period End Date | Apr. 13, 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 |
