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Equity-Based Compensation (Tables) | 9 Months Ended
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Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract] |
Grant Date Fair Value for Awards of Performance Units Inputs | The grant date fair values for awards of performance units with market-based metrics, which were granted in the nine months ended September 30, 2018 and 2017, were determined using a Monte Carlo simulation valuation methodology using the following key inputs:
|  | 2018 |  | 2017
Valuation date stock price based on the February 28, 2018 and March 22, 2017 closing stock prices |  | $34.44 |  | $36.31
Expected volatility |  | 34 | % |  | 36 | %
Risk-free interest rate |  | 2.39 | % |  | 1.46 | %
Term in years |  | 2.84 |  |  | 2.78 |

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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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