| Document and Entity Information | Oct. 06, 2023 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Oct. 06, 2023 |
| Entity File Number | 814-01162 |
| Entity Registrant Name | Venture Lending & Leasing VIII, Inc. |
| Entity Central Index Key | 0001642862 |
| Entity Incorporation, State or Country Code | MD |
| Entity Tax Identification Number | 47-3919702 |
| Entity Address, Address Line One | 104 La Mesa Drive, Suite 102 |
| Entity Address, City or Town | Portola Valley |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94028 |
| City Area Code | 650 |
| Local Phone Number | 234-4300 |
| Entity Emerging Growth Company | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
