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Stock-Based Compensation - Weighted Average Fair Value Per Share of Options Granted, Assumptions (Detail) - Stock Options [Member]
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Volatility 35.00% 38.00% 38.00%
Dividend yield 0.00% 0.00% 0.00%
Life (in years) 4 years 5 months 8 days 4 years 6 months 3 days 4 years 6 months 15 days
Risk-free interest rate 2.54% 1.85% 1.19%