| Document And Entity Information | Oct. 18, 2019 |
| Cover page. | |
| Document Type | 8-K |
| Document Period End Date | Oct. 18, 2019 |
| Entity Registrant Name | FORTINET, INC. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-34511 |
| Entity Tax Identification Number | 77-0560389 |
| Entity Address, Address Line One | 899 Kifer Road |
| Entity Address, City or Town | Sunnyvale |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94086 |
| City Area Code | 408 |
| Local Phone Number | 235-7700 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, $0.001 Par Value |
| Trading Symbol | FTNT |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001262039 |
| Amendment Flag | false |
