| Document and Entity Information | Mar. 01, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Mar. 1, 2021 |
| Entity Registrant Name | KODIAK SCIENCES INC. |
| Entity Central Index Key | 0001468748 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-38682 |
| Entity Tax Identification Number | 27-0476525 |
| Entity Address, Address Line One | 1200 Page Mill Road |
| Entity Address, City or Town | Palo Alto |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94304 |
| City Area Code | (650) |
| Local Phone Number | 281-0850 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Security 12b Title | Common stock, par value $0.0001 |
| Trading Symbol | KOD |
| Security Exchange Name | NASDAQ |
