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Share-Based Compensation - Additional Information (Detail) - USD ($)
1 Months Ended 3 Months Ended 9 Months Ended
Feb. 29, 2020
Sep. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Common stock, authorized shares   6,000,000,000   6,000,000,000   6,000,000,000
Share-based compensation arrangement by share-based payment award performance period       1 year    
2017 Employee Plan [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Shares of common stock reserved for future issuance   4,512,900   4,512,900    
Compensation expense   $ 4,000,000 $ 4,000,000 $ 10,000,000 $ 12,000,000  
Unrecognized compensation costs related to unvested awards   $ 22,000,000   $ 22,000,000    
Unrecognized compensation costs related to unvested awards, weighted-average period       1 year 7 months 6 days    
Total fair value of shares vested       $ 17,000,000 $ 21,000,000  
2017 Employee Plan [Member] | Maximum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Common stock, authorized shares   8,000,000   8,000,000    
2017 Director Plan [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Shares of common stock reserved for future issuance   80,530   80,530    
2017 Director Plan [Member] | Maximum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Common stock, authorized shares   450,000   450,000    
Performance Stock Units ("PSUs") [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Compensation expense   $ 0   $ 0    
Share-based compensation arrangement by share-based payment award performance period 1 year     3 years    
Market capitalization   $ 1,000,000,000   $ 1,000,000,000    
Vesting rights       zero to 200    
Performance Stock Units ("PSUs") [Member] | Tranche Two [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting rights 100%          
Performance Stock Units ("PSUs") [Member] | Maximum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting rights       200%    
Performance Stock Units ("PSUs") [Member] | Maximum [Member] | Tranche Three [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting rights 200%          
Performance Stock Units ("PSUs") [Member] | Minimum [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting rights       0%    
Performance Stock Units ("PSUs") [Member] | Minimum [Member] | Tranche One [Member]            
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]            
Vesting rights 0%