Share-Based Compensation (Tables)
|9 Months Ended|
Sep. 30, 2017
|Share-based Compensation [Abstract]|
|Fair Value Assumptions for Performance Awards||
The fair values of the senior executives' performance share award grants with a TSR modifier for grants in 2017 and 2016 were $64.82 and $38.54, respectively, which were estimated using the Monte Carlo valuation model, and incorporated the following assumptions:
Schedule of Share-based Payment Award, Equity Instruments Other than Options, Valuation Assumptions [Table Text Block]
No definition available.