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Stock-Based Compensation - Black-Scholes-Merton Option Pricing Model for Stock Options Granted (Detail)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Payment Arrangement [Abstract]      
Expected dividend yield 0.00% 0.00% 0.00%
Weighted average expected volatility 51.00% 58.00% 58.00%
Weighted average expected term (years) 6 years 25 days 5 years 11 months 12 days 5 years 10 months 24 days
Weighted average risk-free rate 1.14% 2.26% 2.68%