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Share-based Compensation - Option Grant Fair Value Assumptions (Detail)
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Expected volatility 41.14% 41.63%
Expected dividends 0.00% 0.00%
Expected term (in years) 5 years 11 months 26 days 5 years 11 months 26 days
Risk-free rate 2.55% 2.66%