Intangible Assets - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	Jan. 31, 2021	Apr. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	$ 12,038	$ 11,574
Total definite-lived intangible assets, Accumulated Amortization	(7,602)	(7,199)
Total definite-lived intangible assets, Net Carrying Amount	4,436	4,375
Total Intangible assets, Net Carrying Amount	4,436	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	(2,041)	(1,932)
Total definite-lived intangible assets, Net Carrying Amount	539	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	(194)	(176)
Total definite-lived intangible assets, Net Carrying Amount	6	24
Patents, trademarks, and trade names
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	8,242	8,140
Total definite-lived intangible assets, Accumulated Amortization	(5,367)	(5,091)
Total definite-lived intangible assets, Net Carrying Amount	2,875	3,049
Definite-lived intangible assets excluding patents in progress
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	11,022	10,920
Total definite-lived intangible assets, Accumulated Amortization	(7,602)	(7,199)
Total definite-lived intangible assets, Net Carrying Amount	3,420	3,721
Patents in progress
Finite-Lived Intangible Assets [Line Items]
Total definite-lived intangible assets, Gross Carrying Amount	1,016	654
Total definite-lived intangible assets, Net Carrying Amount	$ 1,016	$ 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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Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

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