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Share-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares available for grant 3,100,000  
Shares reserved for future issuance 22,900,000  
Weighted average grant date value (in dollars per share) $ 188.48 $ 169.24
Employee Stock Purchase Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Number of shares available for grant 702,000  
Shares reserved for future issuance 2,000,000.0  
Percentage of annual compensation participants may contribute 15.00%  
Purchase price as a percentage of closing price on the last day of the quarter for ESPP transactions 85.00%  
Stock Option Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Contractual term 10 years  
Unvested options to purchase (in shares) 1,200,000 1,700,000
Total unrecognized compensation cost $ 148.7  
Weighted average amortization period 2 years 6 months  
Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting period 3 years  
Minimum | Stock Option Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting period 3 years  
Minimum | Restricted Stock Units (RSUs)    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting period 3 years  
Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting period 6 years  
Maximum | Stock Option Plan    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting period 6 years  
Maximum | Restricted Stock Units (RSUs)    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Vesting period 5 years