| Document and Entity Information | Nov. 05, 2020 |
| Document And Entity Information [Line Items] | |
| Entity Registrant Name | ZIX CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0000855612 |
| Document Type | 8-K |
| Document Period End Date | Nov. 5, 2020 |
| Entity Incorporation, State or 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 |
| Entity Emerging Growth Company | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | ZIXI |
| Security Exchange Name | NASDAQ |
| Former Address [Member] | |
| Document And Entity Information [Line Items] | |
| Entity Address, Address Line One | 2711 North Haskell Avenue |
| Entity Address, Address Line Two | Suite 2200 |
| 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 |
