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Share-Based Compensation - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Common stock, authorized shares 6,000,000,000  
2017 Employee Plan [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Shares of common stock reserved for future issuance 6,140,940  
Compensation expense $ 4,000,000 $ 3,000,000
Unrecognized compensation costs related to unvested awards $ 27,000,000  
Unrecognized compensation costs related to unvested awards, weighted-average period 1 year 9 months 18 days  
2017 Employee Plan [Member] | Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Common stock, authorized shares 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 390,154  
2017 Director Plan [Member] | Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Common stock, authorized shares 450,000  
Performance Stock Units ("PSUs") [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Vesting rights zero to 200%  
Performance Stock Units ("PSUs") [Member] | Maximum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Share-based compensation arrangement by share-based payment award performance period 3 years  
Vesting rights 200%  
Performance Stock Units ("PSUs") [Member] | Minimum [Member]    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Share-based compensation arrangement by share-based payment award performance period 2 years  
Market capitalization $ 1,000,000,000  
Vesting rights 0%