Document and Entity Information - shares
6 Months Ended
Jun. 30, 2019
Aug. 05, 2019
Document And Entity Information [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Trading Symbol ZIXI  
Entity Registrant Name ZIX CORP  
Entity Central Index Key 0000855612  
Current Fiscal Year End Date --12-31  
Entity Filer Category Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Common Stock, Shares Outstanding   55,599,329
Entity Current Reporting Status Yes  
Entity Shell Company false  
Entity Interactive Data Current Yes  
Security Exchange Name NASDAQ  
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 2200, 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  
Title of 12(b) Security Common Stock  
Entity Incorporation, State or Country Code TX  
Document Quarterly Report true  
Document Transition Report false