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Stockholders' Equity - Narrative (Details)
 12 Months Ended
Jan. 21, 2019
shares
Dec. 31, 2018
USD ($)
vote
$ / shares
shares
Dec. 31, 2017
shares
Dec. 31, 2016
shares
Oct. 22, 2018
shares
Feb. 29, 2016
USD ($)
Class of Stock [Line Items]            
Shares repurchased in association with tax withholdings on the vesting of RSUs (in shares)   30,119 32,457 94,826    
Class A common stock            
Class of Stock [Line Items]            
Conversion of common stock (in shares)   1        
Common stock number of votes | vote   1        
Amount authorized to be repurchased | $           $ 250,000,000
Additional amount authorized to be repurchased         250,000,000  
Class A common stock | Restricted Stock Units (RSUs)            
Class of Stock [Line Items]            
Treasury stock acquired, average cost (in dollars per share) | $ / shares   $ 112.05        
Adjustments related to tax withholding for share-based compensation | $   $ 3,400,000        
Class A common stock | The 2016 Stock Repurchase Authorization            
Class of Stock [Line Items]            
Remaining authorized repurchase amount | $   $ 233,600,000        
Class B common stock            
Class of Stock [Line Items]            
Percentage of Class B common to total common stock subject to automatic conversion   1.00%        
Common stock number of votes | vote   10        
Subsequent Event | Class B common stock            
Class of Stock [Line Items]            
Number of shares that were agreed to be converted (in shares) 1,000,000          
Percent of shares required to be converted by the end of every two years 15.00%          
Stock conversion, term 2 years          
Percent of shares required to be converted by December 31, 2020 15.00%          
Percent of shares required to be converted by December 31, 2022 30.00%          
Percent of shares required to be converted by December 31, 2024 45.00%