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Stock-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2021
Share-based Payment Arrangement [Abstract] |
Schedule of RSUs and PSUs to be Settled in Common Stock Activity | A summary of the activity for RSUs to be settled in common stock for the nine months ended September 30, 2021 and 2020 is set forth below (shares in thousands):
| 2021 |  | 2020
| RSUs |  | Weighted Average Grant Date Fair Value (Per share) |  | RSUs |  | Weighted Average Grant Date Fair Value (Per share)
Unvested at January 1 | 3,869 |  |  | $37.57 |  | 3,265 |  |  | $35.34
Granted | 945 |  |  | $82.75 |  | 2,008 |  |  | $39.65
Vested | (1,442) |  |  | $36.92 |  | (1,228) |  |  | $35.68
Forfeited | (119) |  |  | $47.23 |  | (114) |  |  | $36.26
Unvested at period ended September 30 | 3,253 |  |  | $50.71 |  | 3,931 |  |  | $37.41
A summary of the activity for PSUs to be settled in common stock for the nine months ended September 30, 2021 and 2020 is set forth below (shares in thousands):
| 2021 |  | 2020
| PSUs |  | Weighted Average Grant Date Fair Value (Per share) |  | PSUs |  | Weighted Average Grant Date Fair Value (Per share)
Unvested at January 1 | 1,047 |  |  | $37.65 |  | 848 |  |  | $33.20
Granted | 174 |  |  | $90.44 |  | 436 |  |  | $34.59
Vested | (268) |  |  | $38.28 |  | (238) |  |  | $17.48
Forfeited | (11) |  |  | $36.90 |  | — |  |  | N/A
Unvested at September 30 | 942 |  |  | $47.27 |  | 1,046 |  |  | $37.35
Grant Date Fair Value for Awards of Performance Units Inputs | The Monte Carlo simulation valuation methodology applied the following key inputs:
|  | 2021 |  | 2020
Valuation date price based on March 25, 2021 and March 26, 2020 closing stock prices of Quanta common stock |  | $83.48 |  | $31.49
Expected volatility |  | 36 | % |  | 34 | %
Risk-free interest rate |  | 0.26 | % |  | 0.35 | %
Term in years |  | 2.77 |  | 2.76

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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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