| Document and Entity Information | Mar. 22, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 22, 2024 |
| Entity Registrant Name | Grayscale Horizen Trust (ZEN) |
| Entity Central Index Key | 0001748945 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Securities Act File Number | 000-56435 |
| Entity Incorporation, State or Country Code | DE |
| Entity Tax Identification Number | 83-6217411 |
| Entity Address, Address Line One | c/o Grayscale Investments, LLC |
| Entity Address, Address Line Two | 290 Harbor Drive, 4th Floor |
| Entity Address, City or Town | Stamford |
| Entity Address, State or Province | CT |
| Entity Address, Postal Zip Code | 06902 |
| City Area Code | 212 |
| Local Phone Number | 668-1427 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(g) Security | Grayscale Horizen Trust (ZEN) Shares |
| Trading Symbol | HZEN |
