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Stock Plans - Summary of Performance Stock Unit Activity (Detail) - Performance Stock Unit Activity - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2018
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]        
Unvested Shares, Beginning Balance 242,186 218,886 242,186 186,621
Granted, Shares   83,819 62,775 98,886
Vested, Shares   (139,478) (41,660) (72,504)
Performance adjustments, Shares   76,960 (35,756) 29,183
Forfeited, Shares (8,659) (2,152)    
Unvested Shares, Ending Balance   238,035 218,886 242,186
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]        
Unvested Weighted Average Grant Date Fair Value, Beginning Balance (dollars per share) $ 55.06 $ 68.43 $ 55.06 $ 46.18
Granted, Weighted Average Grant Date Fair Value (dollars per share)   101.03 84.79 72.73
Vested, Weighted Average Grant Date Fair Value (dollars per share)   44.75 40.23 57.19
Performance adjustments, Weighted Average Grant Date Fair value (dollars per share)   44.24 45.21 57.27
Forfeited, Weighted Average Grant Date Fair Value (dollars per share) $ 44.53 99.82    
Unvested Weighted Average Grant Date Fair Value, Ending Balance (dollars per share)   $ 85.39 $ 68.43 $ 55.06