The change in the net carrying amount of goodwill for the nine months ended September 30, 2023 by segment was as follows (in thousands):


	Steel Mills		Steel Products			Raw Materials		Total
Balance at December 31, 2022	$	675,186	$	2,510,045		$	734,829	$	3,920,060
Acquisitions		-		(2,120	)		-		(2,120	)
Translation		-		4,327			-		4,327
Balance at September 30, 2023	$	675,186	$	2,512,252		$	734,829	$	3,922,267

Nucor completed its most recent annual goodwill impairment testing as of the first day of the fourth quarter of 2022 and concluded that as of such date there was no impairment of goodwill for any of its reporting units.

The annual assessment performed in 2022 for one of the Company’s reporting units, Rebar Fabrication (which is included in the Steel Products segment), used forward-looking projections in future cash flows. The fair value of this reporting unit exceeded its carrying value by approximately 34% in the most recent assessment. If our assessment of the relevant facts and circumstances changes, including if the expected future performance of this reporting unit declines from the most recent assessment, non-cash impairment charges may be required. Total goodwill associated with the Rebar Fabrication reporting unit was $351.5 million as of September 30, 2023 ($347.6 million as of December 31, 2022). 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 $31.3 million as of September 30, 2023 ($36.3 million as of December 31, 2022). 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.

Intangible assets with estimated useful lives of five to 25 years are amortized on a straight-line or accelerated basis and consisted of the following as of September 30, 2023 and December 31, 2022 (in thousands):


	September 30, 2023				December 31, 2022
	Gross Amount		Accumulated Amortization		Gross Amount		Accumulated Amortization
Customer relationships	$	4,175,065	$	1,243,668	$	4,174,724	$	1,087,834
Trademarks and trade names		364,173		159,369		364,106		142,363
Other		109,747		98,975		109,746		96,114
	$	4,648,985	$	1,502,012	$	4,648,576	$	1,326,311

Intangible asset amortization expense in the third quarter of 2023 and 2022 was $58.5 million and $77.2 million, respectively, and $175.7 million and $164.5 million in the first nine months of 2023 and 2022, respectively. Annual amortization expense is estimated to be $232.8 million in 2023; $233.3 million in 2024; $232.3 million in 2025; $229.4 million in 2026; and $225.1 million in 2027.