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Stock-Based Compensation - RSUs to be Settled in Cash (Details) - Restricted Stock Units to be Settled in Cash - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period for RSUs to be settled in cash 3 years    
Amount in cash received for each RSU is equal to the fair value of this number of Quanta common stock shares (in shares) 1    
Compensation expense related to RSUs to be settled in cash $ 1.1 $ 2.6  
Payments to settle liabilities under compensation plan 3.3 $ 2.9  
Accrued liabilities under compensation plan $ 2.4   $ 4.3