GOODWILL AND OTHER INTANGIBLE ASSETS

Goodwill.

During the fourth quarters of 2018, 2017, and 2016, the Company completed its goodwill impairment test using the quantitative assessment. During the second quarter of 2016, in connection with the realignment of the Company’s reporting segments, the Company performed an analysis to determine the allocations of goodwill and test for impairment. Based on these assessments, it determined that the portion of goodwill allocated to the retail branch operations was impaired as the fair value of the reporting unit did not exceed its carrying value resulting in an impairment charge for the Commercial Trailer Products reporting segment of $1.7 million. During the third quarter of 2018, the Company performed an interim impairment analysis after identifying indicators of impairment based on the results of the Aviation and Truck Equipment reporting unit. Based on this assessment, it was determined that all of the goodwill allocated to the Aviation and Truck Equipment reporting unit was impaired resulting in an impairment charge for the Diversified Products reporting segment of $4.9 million. Based on all other assessments performed in each of the last three years, the Company believed it was more likely than not that the fair value of its reporting units were greater than their carrying amount and no additional impairment of goodwill was recognized.

For the year ended December 31, 2018, the changes in the carrying amounts of goodwill were as follows (in thousands):



	Commercial Trailer Products			Diversified Products			Final Mile Products			Total
Balance at December 31, 2016
Goodwill	$	4,288		$	145,742		$	—		$	150,030
Accumulated impairment losses	(1,663		)	—			—			(1,663		)
Net balance at December 31, 2016	2,625			145,742			—			148,367
Acquisition of Supreme	—			—			169,235			169,235
Effects of foreign currency	—			(138		)	—			(138		)
Goodwill impairments during 2017	—			—			—			—
Balance at December 31, 2017
Goodwill	4,288			145,604			169,235			319,127
Accumulated impairment losses	(1,663		)	—			—			(1,663		)
Net balance as of December 31, 2017	2,625			145,604			169,235			317,464
Acquisition of Supreme	—			—			(1,520		)	(1,520		)
Effects of foreign currency	—			84			—			84
Goodwill impairments during 2018	—			(4,944		)	—			(4,944		)
Balance as of December 31, 2018
Goodwill	4,288			145,688			167,715			317,691
Accumulated impairment losses	(1,663		)	(4,944		)	—			(6,607		)
Net balance as of December 31, 2018	$	2,625		$	140,744		$	167,715		$	311,084

Intangible Assets.

As of December 31, 2018, the balances of intangible assets, other than goodwill, were as follows (in thousands):



	Weighted Average Amortization Period	Gross Intangible Assets		Accumulated Amortization			Net Intangible Assets
Tradenames and trademarks	20 years	$	53,103	$	(15,307	)	$	37,796
Customer relationships	13 years	282,736		(116,222		)	166,514
Technology	12 years	14,045		(8,027		)	6,018
Total		$	349,884	$	(139,556	)	$	210,328

As of December 31, 2017, the balances of intangible assets, other than goodwill, were as follows (in thousands):



	Weighted Average Amortization Period	Gross Intangible Assets		Accumulated Amortization			Net Intangible Assets
Tradenames and trademarks	20 years	$	57,894	$	(14,034	)	$	43,860
Customer relationships	10 years	290,415		(105,567		)	184,848
Technology	12 years	16,517		(8,694		)	7,823
Backlog	less than 1 year	2,200		(1,701		)	499
Total		$	367,026	$	(129,996	)	$	237,030

Intangible asset amortization expense was $19.5 million, $17.0 million, and $19.9 million for 2018, 2017, and 2016, respectively. Annual intangible asset amortization expense for the next 5 fiscal years is estimated to be $20.6 million in 2019; $22.1 million in 2020; $23.4 million in 2021; $18.1 million in 2022; and $15.6 million in 2023.