Stock-Based Compensation and Stock Options - Outstanding Options (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance, Shares	975,917	990,064	1,029,103	1,058,411
Granted, Number of Options	122,750	144,650	209,575	242,125
Exercised, Number of Options	(62,997)	(28,225)	(187,815)	(185,173)
Cancelled - forfeited, Number of Options	(1,905)
Cancelled - expired, Number of Options	(329)
Options outstanding, ending balance, Shares	1,033,436	1,099,514	1,033,436	1,099,514
Ending vested and expected to vest, Number of Options	808,294		808,294
Ending exercisable, Number of Options	394,900		394,900
Options outstanding, beginning balance, Weighted Average Exercise Price	$ 57.97	$ 49.84	$ 54.87	$ 45.17
Granted, Weighted Average Exercise Price per Share	87.69	77.93	78.52	78.43
Exercised, Weighted Average Exercise Price per Share	44.83	44.28	40.13	37.67
Cancelled - forfeited, Weighted Average Exercise Price per Share	63.54
Cancelled - expired, Weighted Average Exercise Price per Share	34.78
Options outstanding, ending balance, Weighted Average Exercise Price	62.30	$ 53.66	62.30	$ 53.66
Ending vested and expected to vest, Weighted Average Exercise Price per Share	53.51		53.51
Ending exercisable, Weighted Average Exercise Price per Share	$ 47.18		$ 47.18
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 4 months 13 days
Ending vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 4 months 28 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 6 months
Option outstanding, Aggregate Intrinsic Value	$ 45,161,613		$ 45,161,613
Ending vested and expected to vest, Aggregate Intrinsic Value	22,224,930		22,224,930
Ending exercisable, Aggregate Intrinsic Value	$ 23,230,004		$ 23,230,004