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Schedule of Restricted Stock Units Weighted Average Remaining Contractual Terms (Detail) - Restricted Stock Units
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award      
Outstanding 11 months 15 days 1 year 7 days 11 months 1 day
Expected to vest 11 months 15 days 1 year 7 days 10 months 28 days