| Document and Entity Information | Jun. 12, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | PEGASYSTEMS INC |
| Amendment Flag | false |
| Entity Central Index Key | 0001013857 |
| Current Fiscal Year End Date | --12-31 |
| Document Type | 8-K |
| Document Period End Date | Jun. 12, 2020 |
| Entity File Number | 1-11859 |
| Entity Incorporation State Country Code | MA |
| Entity Tax Identification Number | 04-2787865 |
| Entity Address, Address Line One | 1 Rogers Street |
| Entity Address, City or Town | Cambridge |
| Entity Address, State or Province | MA |
| Entity Address, Postal Zip Code | 02142 |
| City Area Code | 617 |
| Local Phone Number | 374-9600 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common stock, $.01 par value per share |
| Trading Symbol | PEGA |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
