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Stock-Based Compensation - Additional Information (Detail) - USD ($)
$ / shares in Units, $ in Thousands
6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total compensation expense related to unvested stock-based awards granted to employees, officers and directors $ 30,447  
Restricted Stock Units (RSUs) [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Restricted stock units, granted 259,597 376,081
Restricted stock units, weighted average grant date fair value $ 112.56 $ 67.13
Stock Appreciation Rights (SARs) [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Restricted stock units, granted 0 0