| Share-Based Compensation and Cash-Based Incentive Compensation - Schedule of Outstanding Restricted Stock Units Issued to Eligible Employees (Details) - Restricted Stock Units (RSUs) - shares | Sep. 30, 2018 | Dec. 31, 2017 | 
|---|---|---|
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||
| Awards expected to vest by period | 6,610,067 | 5,765,251 | 
| 2018 | ||
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||
| Awards expected to vest by period | 3,657,375 | |
| 2019 | ||
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||
| Awards expected to vest by period | 1,966,359 | |
| 2020 | ||
| Share Based Compensation Arrangement By Share Based Payment Award [Line Items] | ||
| Awards expected to vest by period | 986,333 | 
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- Definition The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date. Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef 
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. No definition available. 
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