Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Summary of Significant Accounting Policies [Line Items]
Uncertain tax positions	$ 0	$ 0	$ 0
Interest or penalties charges recognized	0	0	0
Undistributed loss allocated to holders of convertible preferred shares	0
Total comprehensive loss	$ (21,171,000)	(13,676,000)	(7,382,000)
Previously Reported [Member] | Restated to Correct Errors in Foreign Currency Translation Adjustments [Member]
Summary of Significant Accounting Policies [Line Items]
Total comprehensive loss		$ (9,196,000)	$ (7,070,000)