The change in the net carrying amount of goodwill for the years ended December 31, 2019 and 2018 by segment is as follows:

	(in thousands)
	Steel			Steel			Raw
	Mills			Products			Materials		Total
Balance, December 31, 2017	$	745,484		$	720,997		$	729,577	$	2,196,058
Reclassifications		(153,498	)		153,498			—		—
Translation		—			(11,722	)		—		(11,722	)
Balance, December 31, 2018		591,986			862,773			729,577		2,184,336
Acquisitions		—			12,623			—		12,623
Translation		—			4,104			—		4,104
Balance, December 31, 2019	$	591,986		$	879,500		$	729,577	$	2,201,063

Intangible assets with estimated useful lives of five to 22 years are amortized on a straight-line or accelerated basis and are comprised of the following:

	(in thousands)
	December 31, 2019				December 31, 2018
	Gross		Accumulated		Gross		Accumulated
	Amount		Amortization		Amount		Amortization
Customer relationships	$	1,412,954	$	767,532	$	1,418,250	$	713,656
Trademarks and trade names		162,183		92,258		176,046		87,680
Other		63,807		36,968		67,820		32,276
	$	1,638,944	$	896,758	$	1,662,116	$	833,612

Intangible asset amortization expense was $85.7 million in 2019 ($88.8 million in 2018 and $91.2 million in 2017). Annual amortization expense is estimated to be $83.5 million in 2020, $82.3 million in 2021, $80.7 million in 2022, $79.1 million in 2023 and $79.2 million in 2024.

The Company completed its annual goodwill impairment testing as of the first day of the fourth quarters of 2019, 2018 and 2017 and concluded that as of such dates there was no impairment of goodwill for any of its reporting units. The annual evaluation performed in 2019 used forward-looking projections and included expected improvements in the future cash flows of one of the Company’s reporting units, Rebar Fabrication. The fair value of this reporting unit exceeded its carrying value by approximately 56% in the most recent evaluation. As the reporting unit worked through its more expensive inventory and stabilized its backlog pricing for new projects, the operating results for the reporting unit significantly improved in the second half of 2019. We expect the 2020 operating results of this reporting unit will continue to improve as compared to 2019. If our assessment of the relevant facts and circumstances changes, or the actual performance in this reporting unit falls short of expected results, non-cash impairment charges may be required. Total goodwill associated with the Rebar Fabrication reporting unit as of December 31, 2019 was $356.6 million. An impairment of goodwill may also lead us to record an impairment of other intangible assets. Total finite-lived intangible assets associated with the Rebar Fabrication reporting unit as of December 31, 2019 was $67.2 million.

The Company has monitored one of its reporting units, Grating, for potential triggering events since the impairment assessment performed in the fourth quarter of 2018. Due to lower than expected operating results and anticipated changes to the reporting unit’s business strategy and structure, the Company determined a triggering event occurred in the third quarter of 2019 and performed an impairment assessment. The fair value of the Grating reporting unit exceeded its carrying value by approximately 17% in the most recent assessment. If our assessment of the relevant facts and circumstances changes, or the actual performance of this reporting unit falls short of expected results, non-cash impairment charges may be required. As of December 31, 2019, total goodwill associated with the Grating reporting unit was $36.8 million. As a result of management’s changes to the Grating

reporting unit’s business strategy and structure, the remaining balance of its intangible assets of $3.3 million was written off in the fourth quarter of 2019.

Additionally, a non-cash impairment charge of $8.6 million was taken in the fourth quarter of 2019 on the finite-lived intangible assets, specifically trade names, as they were no longer being utilized.

There are no significant historical accumulated impairment charges, by segment or in the aggregate, related to goodwill.