Stock Based Compensation and Stock Options - Outstanding Options (Detail) - USD ($)	3 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding, beginning balance, Shares	1,064,439	1,143,928
Granted, Number of Options	56,800	77,400
Exercised, Number of Options	(54,238)	(65,921)
Cancelled - forfeited, Number of Options	(920)
Cancelled - expired, Number of Options	(2,827)
Options outstanding, ending balance, Shares	1,063,254	1,151,722
Ending vested and expected to vest, Number of Options	1,028,667
Ending exercisable, Number of Options	432,433
Options outstanding, beginning balance, Weighted Average Exercise Price	$ 39.45	$ 32.02
Granted, Weighted Average Exercise Price per Share	49.40	45.93
Exercised, Weighted Average Exercise Price per Share	30.84	26.67
Cancelled - forfeited, Weighted Average Exercise Price per Share	45.30
Cancelled - expired, Weighted Average Exercise Price per Share	27.03
Options outstanding, ending balance, Weighted Average Exercise Price	40.43	$ 33.24
Ending vested and expected to vest, Weighted Average Exercise Price per Share	40.41
Ending exercisable, Weighted Average Exercise Price per Share	$ 32.91
Option outstanding, Weighted Average Remaining Contractual Life (Years)	3 years 4 months 9 days
Ending vested and expected to vest, Weighted Average Remaining Contractual Life (Years)	3 years 4 months 17 days
Ending exercisable, Weighted Average Remaining Contractual Life (Years)	2 years 5 months 12 days
Option outstanding, Aggregate Intrinsic Value	$ 14,994,783
Ending vested and expected to vest, Aggregate Intrinsic Value	14,511,458
Ending exercisable, Aggregate Intrinsic Value	$ 9,118,958