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Stock-Based Compensation - Options Granted under Company's Stock Incentive Plans, Valuation Assumptions and Fair Values (Detail) - Stock Options [Member] - $ / shares
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Average risk-free interest rate 1.60% 2.89% 1.99% 2.50%
Expected dividend yield 0.00% 0.00% 0.00% 0.00%
Expected life 3 years 6 months 3 years 6 months 3 years 6 months 3 years 6 months
Expected volatility   61.20%    
Weighted average exercise price $ 6.78 $ 2.91 $ 5.69 $ 3.08
Weighted average fair value $ 2.63 $ 1.34 $ 2.26 $ 1.41
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected volatility 51.04%   51.04% 60.80%
Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected volatility 51.37%   54.23% 61.60%