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Stock-Based Compensation - Additional Information (Detail)
$ in Millions
1 Months Ended 12 Months Ended
Nov. 10, 2015
shares
Nov. 25, 2014
shares
Oct. 01, 2005
Sep. 30, 2005
May 31, 2011
May 31, 2010
Jun. 30, 2004
shares
Sep. 30, 2001
May 31, 2000
installment
Dec. 31, 2017
USD ($)
shares
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Share-based compensation expense not yet recognized | $                   $ 296.7    
Expected recognized period (in years)                   2 years 29 days    
Capitalized stock-based compensation expense | $                   $ 6.2 $ 4.2 $ 3.0
2000 Equity Incentive Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of fair market value of common stock on the grant date         85.00%       100.00%      
Stock option expiration from grant date     7 years 10 years                
Vesting period (in years)           4 years            
Number of shares in reserve                   16,636,172    
Number of shares available for grant                   2,423,051    
2000 Director Option Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Percentage of fair market value of common stock on the grant date                 100.00%      
Stock option expiration from grant date                 10 years      
Number of shares in reserve                   594,403    
Number of shares available for grant                   505,646    
Number of Installments | installment                 4      
2001 Supplemental Stock Plan                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Stock option expiration from grant date     7 years 10 years                
Vesting period (in years)               4 years        
Number of shares in reserve                   1,494,275    
Number of shares available for grant                   260,498    
Minimum percentage of fair value of grant               85.00%        
Common stock employee purchase plans                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Number of shares in reserve             500,000          
Number of shares available for grant                   3,265,791    
Yearly increase in shares available for grant (percent)             2.00%          
Number of additional shares authorized 9,020 3,197                    
Percentage of purchase price reductions                   15.00%    
Offering period (in months)             24 months          
Offering interval (in months)             6 months          
Purchase discount from market price (percent)             85.00%          
Restricted Stock Units                        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                        
Restricted stock units vested and released, net | $                   $ 259.1 $ 227.4 $ 157.6