Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Sep. 30, 2015	Mar. 31, 2015
Options
Outstanding at beginning of period	2,892
Granted	145
Exercised	(703)
Cancelled and expired	(1)
Outstanding at end of period	2,333	2,892
Exercisable at end of period	1,696
Options vested and expected to vest at end of period	2,277
Weighted-Average Exercise Price
Outstanding at beginning of period	$ 14.72
Granted	69.50
Exercised	11.33
Cancelled and expired	14.00
Outstanding at end of period	19.16	$ 14.72
Exercisable at end of period	13.76
Options vested and expected to vest at end of period	$ 18.98
Weighted-Average Remaining Contractual Term (years)
Outstanding	5 years 6 months 22 days	5 years 2 months 5 days
Exercisable at end of period	4 years 6 months
Options vested and expected to vest at end of period	5 years 6 months
Aggregate Intrinsic Value
Outstanding at end of period	$ 172,712
Exercisable at end of period	134,674
Options vested and expected to vest at end of period	$ 169,000