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Stock-Based Compensation - Fair Value of Market Performance Units Estimated, Monte Carlo Simulation Model (Detail) - Market Performance Units [Member]
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate, Minimum 2.22% 2.03%
Risk-free interest rate, Maximum 2.43% 2.36%
Estimated volatility factor, Minimum 33.00% 29.00%
Estimated volatility factor, Maximum 44.00% 32.00%
Expected dividends 0.00% 0.00%