| Document and Entity Information | Sep. 24, 2019 |
| Cover [Abstract] | |
| Entity Registrant Name | FINISAR CORP |
| Entity Incorporation State Country Code | DE |
| Amendment Flag | false |
| Entity Central Index Key | 0001094739 |
| Document Type | 8-K |
| Document Period End Date | Sep. 24, 2019 |
| Entity File Number | 000-27999 |
| Entity Tax Identification Number | 94-3038428 |
| Entity Address, Address Line One | 1389 Moffett Park Drive |
| Entity Address, City or Town | Sunnyvale |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94089 |
| City Area Code | (408) |
| Local Phone Number | 548-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, $.001 |
| Trading Symbol | FNSR |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
