Net Loss Per Share - Computation of Earnings Per Share Basic and Diluted (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net loss	$ (21,692)	$ (17,358)	$ (41,929)	$ (33,593)
Net loss available to ordinary shareholders - basic and diluted	$ (21,692)	$ (17,358)	$ (41,929)	$ (33,593)
Denominator:
Weighted-average shares outstanding - basic and diluted	37,657,409	28,123,334	37,223,957	26,774,378
Loss per share - basic and diluted	$ (0.58)	$ (0.62)	$ (1.13)	$ (1.25)