Revenue Recognition - Summary of Net Sales Transferred to Customers at a Point in Time and Over Time (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2020	Apr. 30, 2019
Disaggregation of Revenue [Line Items]
Net sales transferred to customers	$ 34,257	$ 34,225	$ 39,722	$ 39,336	$ 34,748	$ 32,372	$ 37,278	$ 42,152	$ 147,540	$ 146,550
Over Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									142,419	140,302
Point in Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									5,121	6,248
Domestic
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									115,103	116,586
Domestic | Over Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									109,982	110,338
Domestic | Point in Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									5,121	6,248
International
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									32,437	29,964
International | Over Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									32,437	29,964
International | Point in Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									$ 0	$ 0