(9) Intangible Assets:

The following table presents a summary of intangible assets as of July 31, 2018 and April 30, 2018 (in thousands):

	July 31, 2018							April 30, 2018
	Gross							Gross
	Carrying		Accumulated			Net Carrying		Carrying		Accumulated			Net Carrying
	Amount		Amortization			Amount		Amount		Amortization			Amount
Customer relationships	$	92,360	$	(30,719	)	$	61,641	$	92,360	$	(28,252	)	$	64,108
Developed technology		21,130		(9,461	)		11,669		21,130		(8,178	)		12,952
Patents, trademarks, and trade names		56,879		(23,840	)		33,039		56,718		(22,099	)		34,619
Backlog		1,150		(1,150	)		—		1,150		(1,150	)		—
		171,519		(65,170	)		106,349		171,358		(59,679	)		111,679
Patents in progress		879		—			879		855		—			855
Total definite-lived intangible assets		172,398		(65,170	)		107,228		172,213		(59,679	)		112,534
Indefinite-lived intangible assets		226		—			226		226		—			226
Total intangible assets	$	172,624	$	(65,170	)	$	107,454	$	172,439	$	(59,679	)	$	112,760

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, excluding amortization of deferred financing costs, amounted to $5.4 million and $5.7 million for the three months ended July 31, 2018 and 2017, respectively.

Estimated amortization expense of intangible assets for the remainder of fiscal 2019 and succeeding fiscal years is as follows:

Fiscal	Amount
2019	$	16,449
2020		19,114
2021		16,506
2022		14,125
2023		11,762
Thereafter		28,393
Total	$	106,349

On an annual basis, or more frequently if events or changes in circumstances indicate that the asset might be impaired, we evaluate the fair value of the definite and indefinite-lived intangible assets to determine if an impairment charge is required. We performed our most recent annual impairment review as of February 1, 2018. There were no events or changes in circumstances that would indicate the fair value of intangible assets was reduced below its carrying value during the three months ended July 31, 2018, and therefore intangible assets were not tested for impairment.