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Stock-Based Compensation (Tables) | 12 Months Ended
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Dec. 31, 2020
Share-based Payment Arrangement [Abstract] |
Summary of Restricted Stock and RSU to be Settled in Common Stock Activity | A summary of the activity for RSUs to be settled in common stock for the year ended December 31, 2020 is as follows (shares in thousands):
| Shares |  | Weighted Average Grant Date Fair Value (Per share)
Unvested at December 31, 2019 | 3,265 |  |  | $35.34
Granted | 2,029 |  |  | $39.91
Vested | (1,269) |  |  | $35.69
Forfeited | (156) |  |  | $36.67
Unvested at December 31, 2020 | 3,869 |  |  | $37.57
Grant Date Fair Value for Awards of Performance Units Inputs | The grant date fair values of the PSUs were determined as follows: (i) for the portion of the awards based on company financial and operational performance metrics, by multiplying the number of units granted by the closing price of Quanta’s common stock on the date of grant and (ii) for the portion of the awards based on total shareholder return, by utilizing a Monte Carlo simulation valuation methodology. The Monte Carlo simulation valuation methodology applied the following key inputs:
|  | 2020 |  | 2019 |  | 2018
Valuation date price based on March 26, 2020, March 8, 2019 and February 28, 2018 closing stock prices of Quanta common stock |  | $31.49 |  | $35.19 |  | $34.44
Expected volatility |  | 34 | % |  | 25 | % |  | 34 | %
Risk-free interest rate |  | 0.35 | % |  | 2.43 | % |  | 2.39 | %
Term in years |  | 2.76 |  | 2.81 |  | 2.84

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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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- Definition Tabular disclosure of the changes in outstanding nonvested shares. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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