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Stockholders' Equity - Summary of Assumptions Used to Value Stock Option Grants Using Lattice-Binomial Model (Details)
$ / shares in Units, $ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
$ / shares
Sep. 30, 2017
USD ($)
$ / shares
Sep. 30, 2018
USD ($)
$ / shares
Sep. 30, 2017
USD ($)
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Share-based payment award, expiration period (in years)     10 years  
Dividend yield 0.00% 0.00% 0.00% 0.00%
Expected volatility 40.00% 34.00%    
Risk-free interest rate 2.90% 2.24%    
Suboptimal exercise factor 2.97 2.58    
Weighted-average fair value (in dollars per share) | $ / shares $ 182.45 $ 72.98 $ 153.84 $ 67.23
Stock-based compensation expense $ 82,316 $ 44,763 $ 231,943 $ 133,679
Total income tax impact on provision (in thousands) $ 18,036 $ 14,428 $ 49,617 $ 43,606
Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected volatility     40.00% 34.00%
Risk-free interest rate     2.61% 2.24%
Suboptimal exercise factor     2.80 2.48
Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected volatility     42.00% 37.00%
Risk-free interest rate     2.90% 2.45%
Suboptimal exercise factor     2.97 2.58