Common Stock and Stockholders' Equity - Narrative (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Dec. 31, 2014	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Class of Stock [Line Items]
Stock-based compensation expense		$ 13,833	$ 10,222	$ 24,860	$ 19,845
Unrecognized stock-based compensation cost related to outstanding unvested stock awards		22,700		$ 22,700
Stock-based compensation cost expected to be recognized over weighted-average period				2 years 2 months 24 days
Expected to vest unrecognized stock-based compensation cost related to outstanding unvested stock options		$ 115,300		$ 115,300
Unvested Stock Options
Class of Stock [Line Items]
Stock based compensation cost is expected to be recognized over a weighted-average period				2 years 8 months 25 days
ESPP shares
Class of Stock [Line Items]
Shares reserved for issuance under plan (in shares)	1,000,000
Additional shares available for issuance under the plan (in shares)	500,000
Percentage of common stock shares increased under the plan	1.00%
Common stock purchased under Employee Stock Purchase Plan (in shares)		101,493		82,851
Stock-based compensation expense		$ 1,100	$ 600	$ 1,500	$ 1,000
Shares available for issuance (in shares)		2,346,386		2,346,386
2008 Equity Incentive Plan
Class of Stock [Line Items]
Shares available for issuance (in shares)		0		0
2014 Equity Incentive Plan
Class of Stock [Line Items]
Shares reserved for issuance under plan (in shares)	5,000,000
Shares available for issuance (in shares)		11,635,171		11,635,171
Shares available for grant under plan (in shares)	5,184,878
Increase in shares available under plan, percentage of outstanding common stock shares	5.00%