Stock-Based Compensation and Stock Options - Stock Options Outstanding and Exercisable (Detail) - $ / shares	6 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Outstanding Options	990,064	1,000,830	1,058,411	1,053,307	1,063,254	1,064,439
Weighted Average Remaining Contractual Life	3 years 5 months 8 days
Outstanding Options – Weighted Average Exercise Price	$ 49.84	$ 47.05	$ 45.17	$ 41.81	$ 40.43	$ 39.45
Exercisable Options – Number of Exercisable Options	377,145
Exercisable Options – Weighted Average Exercise Price	$ 38.26
Range of Exercise Price, $20.08 to $38.70 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	20.08
Range of Exercise Price, upper limit	$ 38.70
Number of Outstanding Options	254,229
Weighted Average Remaining Contractual Life	2 years 2 months 8 days
Outstanding Options – Weighted Average Exercise Price	$ 29.29
Exercisable Options – Number of Exercisable Options	190,458
Exercisable Options – Weighted Average Exercise Price	$ 27.97
Range of Exercise Price, $38.71 to $49.40 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Range of Exercise Price, lower limit	38.71
Range of Exercise Price, upper limit	$ 49.40
Number of Outstanding Options	256,185
Weighted Average Remaining Contractual Life	3 years 3 months 21 days
Outstanding Options – Weighted Average Exercise Price	$ 46.41
Exercisable Options – Number of Exercisable Options	134,847
Exercisable Options – Weighted Average Exercise Price	$ 45.54
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	355,025
Weighted Average Remaining Contractual Life	3 years 9 months 14 days
Outstanding Options – Weighted Average Exercise Price	$ 58.05
Exercisable Options – Number of Exercisable Options	51,840
Exercisable Options – Weighted Average Exercise Price	$ 57.10
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	124,625
Weighted Average Remaining Contractual Life	5 years 2 months 26 days
Outstanding Options – Weighted Average Exercise Price	$ 75.47
Exercisable Options – Number of Exercisable Options	0
Exercisable Options – Weighted Average Exercise Price	$ 0