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Stock-Based Compensation - Fair Value of Market Performance Units Estimated, Monte Carlo Simulation Model (Detail) - Market Performance Units [Member]
9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Risk-free interest rate, Minimum 1.61% 2.19%
Risk-free interest rate, Maximum 1.88% 2.84%
Estimated volatility factor, Minimum 40.00% 25.00%
Estimated volatility factor, Maximum 54.00% 28.00%
Expected dividends 0.00% 0.00%