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Stock-based Compensation - Summary of Stock Award Activity (Detail) - Stock Awards [Member] - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Shares, Beginning Balance 87,334    
Granted, Shares 65,278    
Vested, Shares (36,115)    
Forfeited, Shares (9,146)    
Shares, Ending Balance 107,351 87,334  
Unvested Weighted Average Grant Date Fair Value, Beginning Balance $ 80.78    
Granted, Weighted Average Grant Date Fair Value 98.46 $ 89.12 $ 72.06
Vested, Weighted Average Grant Date Fair Value 70.49    
Forfeited, Weighted Average Grant Date Fair Value 84.64    
Unvested Weighted Average Grant Date Fair Value, Ending Balance $ 94.66 $ 80.78