| Document and Entity Information | Aug. 31, 2020 |
| Cover [Abstract] | |
| Entity Registrant Name | MANTECH INTERNATIONAL CORP |
| Amendment Flag | false |
| Entity Central Index Key | 0000892537 |
| Document Type | 8-K |
| Document Period End Date | Aug. 31, 2020 |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 000-49604 |
| Entity Tax Identification Number | 22-1852179 |
| Entity Address, Address Line One | 2251 Corporate Park Drive |
| Entity Address, City or Town | Herndon |
| Entity Address, State or Province | VA |
| Entity Address, Postal Zip Code | 20171 |
| City Area Code | (703) |
| Local Phone Number | 218-6000 |
| Security 12b Title | Class A Common Stock |
| Trading Symbol | MANT |
| Security Exchange Name | NASDAQ |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
