| Document and Entity Information | Dec. 16, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | SYNOPSYS INC |
| Amendment Flag | false |
| Entity Central Index Key | 0000883241 |
| Document Type | 8-K |
| Document Period End Date | Dec. 16, 2020 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 000-19807 |
| Entity Tax Identification Number | 56-1546236 |
| Entity Address, Address Line One | 690 East Middlefield Road |
| Entity Address, City or Town | Mountain View |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94043 |
| City Area Code | (650) |
| Local Phone Number | 584-5000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock ($0.01 par value) |
| Trading Symbol | SNPS |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
