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Stock-Based Compensation and Stock Options - Stock Options Outstanding and Exercisable (Detail) - $ / shares
6 Months Ended
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]            
Number of Outstanding Options 975,917 1,017,494 1,029,103 990,064 1,000,830 1,058,411
Weighted Average Remaining Contractual Life 3 years 3 months 18 days          
Outstanding Options – Weighted Average Exercise Price $ 57.97 $ 55.54 $ 54.87 $ 49.84 $ 47.05 $ 45.17
Exercisable Options – Number of Exercisable Options 426,263          
Exercisable Options – Weighted Average Exercise Price $ 45.88          
Range of Exercise Price, $21.87 to $48.35 [Member]            
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]            
Range of Exercise Price, lower limit 21.87          
Range of Exercise Price, upper limit $ 48.35          
Number of Outstanding Options 285,745          
Weighted Average Remaining Contractual Life 2 years 3 months 10 days          
Outstanding Options – Weighted Average Exercise Price $ 37.55          
Exercisable Options – Number of Exercisable Options 256,481          
Exercisable Options – Weighted Average Exercise Price $ 36.58          
Range of Exercise Price, $48.36 to $57.75 [Member]            
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]            
Range of Exercise Price, lower limit 48.36          
Range of Exercise Price, upper limit $ 57.75          
Number of Outstanding Options 262,904          
Weighted Average Remaining Contractual Life 3 years 14 days          
Outstanding Options – Weighted Average Exercise Price $ 55.07          
Exercisable Options – Number of Exercisable Options 110,308          
Exercisable Options – Weighted Average Exercise Price $ 55.48          
Range of Exercise Price, $57.76 to $77.93 [Member]            
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]            
Range of Exercise Price, lower limit 57.76          
Range of Exercise Price, upper limit $ 77.93          
Number of Outstanding Options 309,586          
Weighted Average Remaining Contractual Life 3 years 7 months 6 days          
Outstanding Options – Weighted Average Exercise Price $ 69.07          
Exercisable Options – Number of Exercisable Options 46,812          
Exercisable Options – Weighted Average Exercise Price $ 63.03          
Range of Exercise Price, $77.94 to $88.22 [Member]            
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]            
Range of Exercise Price, lower limit 77.94          
Range of Exercise Price, upper limit $ 88.22          
Number of Outstanding Options 117,682          
Weighted Average Remaining Contractual Life 5 years 7 months 2 days          
Outstanding Options – Weighted Average Exercise Price $ 84.83          
Exercisable Options – Number of Exercisable Options 12,662          
Exercisable Options – Weighted Average Exercise Price $ 87.49