Common Stock and Stockholders' Equity - Schedule of Stock Option and RSU Award Activities (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Mar. 31, 2017
Number of Shares
Beginning balance (in shares)	4,607
Stock options granted (in shares)	475
Stock options exercised (in shares)	(1,386)
Stock options canceled/forfeited (in shares)	(246)
Ending balance (in shares)	3,450	4,607
Weighted- Average Exercise Price
Beginning balance (in usd per share)	$ 17.49
Stock options granted (in usd per share)	45.27
Stock options exercised (in usd per share)	14.67
Stock options canceled/forfeited (in usd per share)	26.20
Ending balance (in usd per share)	$ 21.83	$ 17.49
Weighted- Average Remaining Contractual Term (in years)
Weighted- Average Remaining Contractual Term (in years)	6 years 10 months 3 days	7 years 1 month 5 days
Aggregate Intrinsic Value
Beginning aggregate intrinsic value, outstanding	$ 90,339
Stock options exercised	42,151
Ending aggregate intrinsic value, outstanding	$ 124,015	$ 90,339
Number of Shares
Beginning balance (in shares)	1,978
RSUs granted (in shares)	1,001
RSUs vested (in shares)	(587)
RSUs canceled/forfeited (in shares)	(354)
Ending balance (in shares)	2,038	1,978
Weighted- Average Grant Date Fair Value
Beginning balance (in usd per share)	$ 29.32
RSUs granted (in usd per share)	45.59
RSUs vested (in usd per share)	30.89
RSUs canceled/forfeited (in usd per share)	32.02
Ending balance (in usd per share)	$ 36.40	$ 29.32
Weighted- Average Remaining Contractual Term (in years)
Weighted- Average Remaining Contractual Term (in years)	2 years 8 months 12 days	2 years 9 months 18 days
Aggregate Intrinsic Value
Beginning aggregate intrinsic value, outstanding	$ 73,309
Ending aggregate intrinsic value, outstanding	$ 117,718	$ 73,309