The change in the net carrying amount of goodwill for the six months ended July 4, 2020 by segment was as follows (in thousands):

	Steel Mills		Steel Products			Raw Materials		Total
Balance at December 31, 2019	$	591,986	$	879,500		$	729,577	$	2,201,063
Other		-		(821	)		-		(821	)
Translation		-		(10,098	)		-		(10,098	)
Balance at July 4, 2020	$	591,986	$	868,581		$	729,577	$	2,190,144

Nucor completed its most recent annual goodwill impairment testing during the fourth quarter of 2019 and concluded that as of such time there was no impairment of goodwill for any of its reporting units.

The assessment 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 assessment. The reporting unit’s profitability in the first half of 2020 significantly increased from the first half of 2019. We expect the 2020 operating results of the Rebar Fabrication reporting unit will continue to improve compared to 2019. 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. Total goodwill associated with the Rebar Fabrication reporting unit was $347.8 million as of July 4, 2020 ($356.6 million as of December 31, 2019). 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 were $61.3 million as of July 4, 2020 ($67.2 million as of December 31, 2019). There have been no triggering events requiring an interim assessment for impairment of the Rebar Fabrication reporting unit since the most recent annual goodwill impairment testing date.

Due to lower than expected operating results and anticipated changes to the Grating 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 that 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. Total goodwill associated with the Grating reporting unit was $36.5 million as of July 4, 2020 ($36.8 million as of December 31, 2019).

Intangible assets with estimated useful lives of five to 22 years are amortized on a straight-line or accelerated basis and were comprised of the following as of July 4, 2020 and December 31, 2019 (in thousands):

	July 4, 2020				December 31, 2019
	Gross Amount		Accumulated Amortization		Gross Amount		Accumulated Amortization
Customer relationships	$	1,411,626	$	803,415	$	1,412,954	$	767,532
Trademarks and trade names		161,926		96,187		162,183		92,258
Other		63,822		39,335		63,807		36,968
	$	1,637,374	$	938,937	$	1,638,944	$	896,758

Intangible asset amortization expense in the second quarter of 2020 and 2019 was $20.7 million and $21.2 million, respectively, and was $42.2 million and $42.7 million in the first six months of 2020 and 2019, respectively. Annual amortization expense is estimated to be $83.5 million in 2020; $82.3 million in 2021; $80.7 million in 2022; $80.0 million in 2023; and $79.2 million in 2024.