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Stock-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2020
Share-based Payment Arrangement [Abstract] |
Grant Date Fair Value for Awards of Performance Units Inputs | The Monte Carlo simulation valuation methodology applied the following key inputs:
|  | 2020 |  | 2019
Valuation date price based on March 26, 2020 and March 8, 2019 closing stock prices of Quanta common stock |  | $31.49 |  | $35.19
Expected volatility |  | 34 | % |  | 25 | %
Risk-free interest rate |  | 0.35 | % |  | 2.43 | %
Term in years |  | 2.76 |  | 2.81

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- Definition Schedule Of Share Based Payment Award, Equity Instruments Other Than Options, Valuation Assumptions [Table Text Block] + References No definition available. + Details
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