| Document and Entity Information | Sep. 11, 2019 |
| Cover [Abstract] | |
| Entity Registrant Name | ANSYS INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001013462 |
| Document Type | 8-K |
| Document Period End Date | Sep. 11, 2019 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 0-20853 |
| Entity Tax Identification Number | 04-3219960 |
| Entity Address, Address Line One | 2600 ANSYS Drive |
| Entity Address, City or Town | Canonsburg |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 15317 |
| City Area Code | (844) |
| Local Phone Number | 462-6797 |
| 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 per share |
| Trading Symbol | ANSS |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
