| Document and Entity Information | Jun. 14, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | PROOFPOINT INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001212458 |
| Document Type | 8-K |
| Document Period End Date | Jun. 14, 2021 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-35506 |
| Entity Tax Identification Number | 51-0414846 |
| Entity Address, Address Line One | 925 West Maude Ave |
| Entity Address, City or Town | Sunnyvale |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94085 |
| City Area Code | (408) |
| Local Phone Number | 517-4710 |
| Security 12b Title | Common Stock |
| Trading Symbol | PFPT |
| Security Exchange Name | NASDAQ |
| Written Communications | false |
| Soliciting Material | true |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
