Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Other Commitments [Line Items]
Contractual obligation remaining commitments including cancellation provisions	$ 3,600,000
Amounts associated with indemnifications	0
Maximum [Member]
Other Commitments [Line Items]
Royalty payable upon completion of first commercial sale	$ 1,000,000
Royalty payment obligations expiration period	90 days
Indemnification Guarantee [Member]
Other Commitments [Line Items]
Contingent liabilities	$ 0	$ 0