| Document and Entity Information | Nov. 07, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | ZIX CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0000855612 |
| Document Type | 8-K |
| Document Period End Date | Nov. 7, 2021 |
| Entity Incorporation State Country Code | TX |
| Entity File Number | 0-17995 |
| Entity Tax Identification Number | 75-2216818 |
| Entity Address, Address Line One | 2711 North Haskell Avenue |
| Entity Address, Address Line Two | Suite 2300 |
| Entity Address, Address Line Three | LB 36 |
| Entity Address, City or Town | Dallas |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 75204-2960 |
| City Area Code | (214) |
| Local Phone Number | 370-2000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | ZIXI |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
