| Document and Entity Information | Apr. 30, 2024 |
| Document And Entity Information [Line Items] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001280784 |
| Document Type | 8-K |
| Document Period End Date | Apr. 30, 2024 |
| Entity Registrant Name | Hercules Capital, Inc. |
| Entity Incorporation State Country Code | MD |
| Entity File Number | 814-00702 |
| Entity Tax Identification Number | 74-3113410 |
| Entity Address, Address Line One | 1 North B Street |
| Entity Address, Address Line Two | Suite 2000 |
| Entity Address, City or Town | San Mateo |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94401 |
| City Area Code | (650) |
| Local Phone Number | 289-3060 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Common Stock [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | Common Stock, par value $0.001 per share |
| Trading Symbol | HTGC |
| Security Exchange Name | NYSE |
| Deferrable Notes [Member] | |
| Document And Entity Information [Line Items] | |
| Security 12b Title | 6.25% Notes due 2033 |
| Trading Symbol | HCXY |
| Security Exchange Name | NYSE |
