Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Options
Outstanding at beginning of period	1,646
Granted	155
Exercised	(460)
Cancelled and expired	(59)
Outstanding at end of period	1,282	1,646
Exercisable at end of period	965
Options vested and expected to vest at end of period	1,259
Weighted Average Exercise Price
Outstanding at beginning of period	$ 32.09
Granted	143.52
Exercised	20.23
Cancelled and expired	98.21
Outstanding at end of period	46.81	$ 32.09
Exercisable at end of period	24.88
Options vested and expected to vest at end of period	$ 46.18
Weighted Average Remaining Contractual Term (years)
Outstanding	5 years 3 months 21 days	5 years 5 months 15 days
Exercisable at end of period	4 years 3 months 14 days
Options vested and expected to vest at end of period	5 years 3 months 7 days
Aggregate Intrinsic Value
Outstanding at end of period	$ 313,158
Exercisable at end of period	256,891
Options vested and expected to vest at end of period	$ 308,252