Intangible Assets

12 Months Ended

Apr. 30, 2021

Goodwill And Intangible Assets Disclosure [Abstract]

6. Intangible Assets

The following table summarizes intangible assets as of April 30, 2021 and 2020 (in thousands):

	April 30, 2021							April 30, 2020
	Gross							Gross
	Carrying		Accumulated			Net Carrying		Carrying		Accumulated			Net Carrying
	Amount		Amortization			Amount		Amount		Amortization			Amount
Customer relationships	$	89,980	$	(60,347	)	$	29,633	$	89,980	$	(51,049	)	$	38,931
Developed technology		21,588		(14,456	)		7,132		21,588		(12,529	)		9,059
Patents, trademarks, and trade names		50,007		(34,308	)		15,699		49,697		(29,229	)		20,468
Backlog		1,150		(1,150	)		—		1,150		(1,150	)		—
		162,725		(110,261	)		52,464		162,415		(93,957	)		68,458
Patents in progress		749		—			749		490		—			490
Total definite-lived intangible assets		163,474		(110,261	)		53,213		162,905		(93,957	)		68,948
Indefinite-lived intangible assets		430		—			430		204		—			204
Total intangible assets	$	163,904	$	(110,261	)	$	53,643	$	163,109	$	(93,957	)	$	69,152

We amortize intangible assets with determinable lives over a weighted-average period of approximately five years. The weighted-average periods of amortization by intangible asset class is approximately five years for customer relationships, six years for developed technology, and five years for patents, trademarks, and trade names. Amortization expense amounted to $16.3 million, $18.9 million, and $21.6 million for the fiscal years ended April 30, 2021, 2020, and 2019, respectively.

The following table represents future expected amortization expense as of April 30, 2021 (in thousands):

Fiscal	Amount
2022		13,876
2023		11,428
2024		9,689
2025		6,047
2026		4,954
Thereafter		6,470
Total	$	52,464

We did not record any impairment charges for long-lived intangible assets in the fiscal years ended April 30, 2021, 2020, and 2019, respectively, excluding the goodwill impairment charges noted below.