Stock-Based Compensation and Stock Options - Outstanding Options (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance, Shares	990,064	1,053,307	1,058,411	1,064,439
Granted, Number of Options	144,650	145,150	242,125	261,750
Exercised, Number of Options	(28,225)	(76,122)	(185,173)	(197,230)
Cancelled - forfeited, Number of Options	(5,811)
Cancelled - expired, Number of Options	(1,164)
Options outstanding, ending balance, Shares	1,099,514	1,121,527	1,099,514	1,121,527
Ending vested and expected to vest, Number of Options	975,502		975,502
Ending exercisable, Number of Options	381,646		381,646
Options outstanding, beginning balance, Weighted Average Exercise Price	$ 49.84	$ 41.81	$ 45.17	$ 39.45
Granted, Weighted Average Exercise Price per Share	77.93	59.32	78.43	56.72
Exercised, Weighted Average Exercise Price per Share	44.28	41.73	37.67	35.94
Cancelled - forfeited, Weighted Average Exercise Price per Share	53.70
Cancelled - expired, Weighted Average Exercise Price per Share	40.97
Options outstanding, ending balance, Weighted Average Exercise Price	53.66	$ 44.08	53.66	$ 44.08
Ending vested and expected to vest, Weighted Average Exercise Price per Share	42.79		42.79
Ending exercisable, Weighted Average Exercise Price per Share	$ 38.79		$ 38.79
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 5 months 8 days
Ending vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 14 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 7 months 17 days
Option outstanding, Aggregate Intrinsic Value	$ 37,059,875		$ 37,059,875
Ending vested and expected to vest, Aggregate Intrinsic Value	34,585,792		34,585,792
Ending exercisable, Aggregate Intrinsic Value	$ 18,536,176		$ 18,536,176