Stock-based Compensation - Summary of Weighted-Average Assumptions Using Black-Scholes Option-Pricing Model (Detail) - Time-Based Options and SARs [Member] |
12 Months Ended | ||
---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
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Share-based Compensation Arrangement by Share-based Payment Award [Line Items] | |||
Expected term to exercise (years), Time-Based awards | 4 years | 4 years | 4 years |
Expected volatility, Time-Based awards | 25.61% | 27.64% | 26.63% |
Risk-free interest rate, Time-Based awards | 1.92% | 1.30% | 1.42% |
Expected dividend yield, Time-Based awards | 0.73% | 0.82% | 0.74% |