Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Oct. 31, 2020	Apr. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	$ 11,925	$ 11,574
Total definite-lived intangible assets, Accumulated Amortization	(7,467)	(7,199)
Total definite-lived intangible assets, Net Carrying Amount	4,458	4,375
Total Intangible assets, Net Carrying Amount	4,458	4,375
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	2,580	2,580
Total definite-lived intangible assets, Accumulated Amortization	(2,004)	(1,932)
Total definite-lived intangible assets, Net Carrying Amount	576	648
Developed technology
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	200	200
Total definite-lived intangible assets, Accumulated Amortization	(188)	(176)
Total definite-lived intangible assets, Net Carrying Amount	12	24
Patents, trademarks, and trade names
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	8,210	8,140
Total definite-lived intangible assets, Accumulated Amortization	(5,275)	(5,091)
Total definite-lived intangible assets, Net Carrying Amount	2,935	3,049
Definite-lived intangible assets excluding patents in progress
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	10,990	10,920
Total definite-lived intangible assets, Accumulated Amortization	(7,467)	(7,199)
Total definite-lived intangible assets, Net Carrying Amount	3,523	3,721
Patents in progress
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	935	654
Total definite-lived intangible assets, Net Carrying Amount	$ 935	$ 654

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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