10. Intangible Assets

The following table presents a summary of intangible assets as of April 30, 2018 and 2017 (in thousands):

	April 30, 2018							April 30, 2017
	Gross							Gross
	Carrying		Accumulated			Net Carrying		Carrying		Accumulated			Net Carrying
	Amount		Amortization			Amount		Amount		Amortization			Amount
Customer relationships (a)	$	92,360	$	(28,252	)	$	64,108	$	105,260	$	(16,463	)	$	88,797
Developed technology		21,130		(8,178	)		12,952		19,430		(5,436	)		13,994
Patents, trademarks, and trade names		56,718		(22,099	)		34,619		53,308		(15,619	)		37,689
Backlog		1,150		(1,150	)		—		1,150		(1,150	)		—
		171,358		(59,679	)		111,679		179,148		(38,668	)		140,480
Patents in progress		855		—			855		611		—			611
Total definite-lived intangible assets		172,213		(59,679	)		112,534		179,759		(38,668	)		141,091
Indefinite-lived intangible assets		226		—			226		226		—			226
Total intangible assets	$	172,439	$	(59,679	)	$	112,760	$	179,985	$	(38,668	)	$	141,317

(a)	Changes to the gross carrying amount of customer relationships is related to purchase accounting adjustments. For more information regarding the changes in valuation of customer relations, see Note 2 — Acquisitions to our consolidated financial statements.

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 $21.0 million, $20.1 million, and $10.7 million for the fiscal years ended April 30, 2018, 2017, and 2016, respectively.

The following table represents future expected amortization expense as of April 30, 2018, which will primarily be recorded in our Outdoor Products & Accessories segment (in thousands):

Fiscal	Amount
2019	$	21,971
2020		19,095
2021		16,488
2022		14,109
2023		11,747
Thereafter		28,269
Total	$	111,679