| Cover | Aug. 11, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Aug. 11, 2021 |
| Entity File Number | 000-26495 |
| Entity Registrant Name | CYREN LTD. |
| Entity Central Index Key | 0001084577 |
| Entity Tax Identification Number | 00-0000000 |
| Entity Incorporation, State or Country Code | L3 |
| Entity Address, Address Line One | 10 Ha-Menofim St. |
| Entity Address, Address Line Two | 5th Floor |
| Entity Address, City or Town | Herzliya |
| Entity Address, Country | IL |
| Entity Address, Postal Zip Code | 4672561 |
| City Area Code | 972 |
| Local Phone Number | 9–863–6888 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Ordinary Shares, par value ILS 0.15 per share |
| Trading Symbol | CYRN |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
