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Summary of Non-Vested Restricted Stock Activity (Detail) - Non-Vested Restricted Stock - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares, Non-vested beginning balance 3,062,602    
Shares, Granted 173,940    
Shares, Vested (32,000)    
Shares, Forfeited (12,837)    
Shares, Non-vested ending balance 3,191,705 3,062,602  
Weighted-Average Grant Date Fair Value, Non-vested beginning balance $ 48.72    
Weighted-Average Grant Date Fair Value, Granted 151.58 $ 167.06 $ 149.47
Weighted-Average Grant Date Fair Value, Vested 67.54    
Weighted-Average Grant Date Fair Value, Forfeited 148.43    
Weighted-Average Grant Date Fair Value, Non-vested ending balance $ 68.63 $ 48.72