Property, Plant, and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020	Apr. 30, 2019
Property Plant And Equipment [Line Items]
Depreciation	$ 3,500,000	$ 3,400,000	$ 2,800,000
Leasehold improvements	$ 2,273,000	2,054,000
Columbia, Missouri
Property Plant And Equipment [Line Items]
Leasehold improvements		2,200,000
Impairment of leasehold improvement		$ 713,000