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Stock-Based Compensation - Summary of Mastech's Restricted Stock Unit Activity (Detail) - Restricted Stock Units Activity [Member] - shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Beginning outstanding balance 33,285 34,380 30,500
Awarded 11,475 16,365 25,380
Released (13,917) (17,460) (21,500)
Forfeited 0    
Ending outstanding balance 30,843 33,285 34,380