Share-Based Compensation - Summary of Activity Under Share-Based Compensation Plans (Parenthetical) (Detail) - shares |
12 Months Ended | |
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Dec. 31, 2017 |
Dec. 31, 2016 |
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| Market condition awards [Member] | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Outstanding SARs | 100,000 | 100,000 |
| Performance condition SARs [Member] | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Outstanding SARs | 3,100,000 | 2,900,000 |
| Exercisable SARs | 1,500,000 | |
| Performance Based Stock Unit Awards [Member] | Maximum [Member] | ||
| Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | ||
| Number of share based payment awards other than options that can vest maximum | 134,388 |
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- Definition Share based compensation arrangement by share based payment award equity instruments other than options maximum amount that can vest. No definition available.
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- Definition The number of exercisable stock appreciation rights (SARs). No definition available.
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- Definition The number of outstanding stock appreciation rights (SARs). No definition available.
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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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