v3.8.0.1
Document and Entity Information Document - shares
9 Months Ended
Sep. 30, 2017
Oct. 31, 2017
Entity Information [Line Items]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Sep. 30, 2017  
Document Fiscal Year Focus 2017  
Document Fiscal Period Focus Q3  
Trading Symbol MANT  
Entity Registrant Name MANTECH INTERNATIONAL CORP  
Entity Central Index Key 0000892537  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Class A common stock    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   25,804,662
Class B common stock    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   13,189,245