Stock-Based Compensation and Stock Options - Stock Options Outstanding and Exercisable (Detail) - $ / shares	9 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Outstanding Options	1,033,436	975,917	1,029,103	1,099,514	990,064	1,058,411
Weighted Average Remaining Contractual Life	3 years 4 months 13 days
Outstanding Options – Weighted Average Exercise Price	$ 62.30	$ 57.97	$ 54.87	$ 53.66	$ 49.84	$ 45.17
Exercisable Options – Number of Exercisable Options	394,900
Exercisable Options – Weighted Average Exercise Price	$ 47.18
Range of Exercise Price, $21.87 to $49.40 [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	$ 49.40
Number of Outstanding Options	287,621
Weighted Average Remaining Contractual Life	2 years 3 months 3 days
Outstanding Options – Weighted Average Exercise Price	$ 39.58
Exercisable Options – Number of Exercisable Options	249,975
Exercisable Options – Weighted Average Exercise Price	$ 38.29
Range of Exercise Price, $49.41 to $59.32 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	49.41
Range of Exercise Price, upper limit	$ 59.32
Number of Outstanding Options	316,197
Weighted Average Remaining Contractual Life	2 years 10 months 24 days
Outstanding Options – Weighted Average Exercise Price	$ 57.32
Exercisable Options – Number of Exercisable Options	105,756
Exercisable Options – Weighted Average Exercise Price	$ 57.70
Range of Exercise Price, $59.33 to $87.49 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	59.33
Range of Exercise Price, upper limit	$ 87.49
Number of Outstanding Options	278,943
Weighted Average Remaining Contractual Life	4 years 3 months 25 days
Outstanding Options – Weighted Average Exercise Price	$ 77.60
Exercisable Options – Number of Exercisable Options	39,169
Exercisable Options – Weighted Average Exercise Price	$ 75.48
Range of Exercise Price, $87.50 to $88.22 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	87.50
Range of Exercise Price, upper limit	$ 88.22
Number of Outstanding Options	150,675
Weighted Average Remaining Contractual Life	4 years 8 months 15 days
Outstanding Options – Weighted Average Exercise Price	$ 87.79
Exercisable Options – Number of Exercisable Options	0
Exercisable Options – Weighted Average Exercise Price	$ 0