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, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2019	Apr. 30, 2018
Disaggregation of Revenue [Line Items]
Net sales transferred to customers	$ 34,748	$ 32,372	$ 37,278	$ 42,152	$ 44,508	$ 38,190	$ 41,471	$ 33,881	$ 146,550	$ 158,050
Over Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									140,302
Point in Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									6,248
Domestic
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									116,586
Domestic | Over Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									110,338
Domestic | Point in Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									6,248
International
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									29,964
International | Over Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									29,964
International | Point in Time
Disaggregation of Revenue [Line Items]
Net sales transferred to customers									$ 0