Note 7—Goodwill and Intangible Assets

The change in goodwill by segment for 2018 and 2017 was as follows (in thousands):


	Power		Pipeline		Utilities		Transmission		Civil		Total
Balance at January 1, 2017	$	24,512	$	42,252	$	20,312	$	—	$	40,150	$	127,226
Goodwill acquired during the year		—		9,269		17,000		—		—		26,269
Purchase price allocation adjustments		(121)		—		—		—		—		(121)
Balance at January 1, 2018	$	24,391	$	51,521	$	37,312	$	—	$	40,150	$	153,374
Goodwill acquired during the year		1,542		764		—		50,479		—		52,785
Balance at December 31, 2018	$	25,933	$	52,285	$	37,312	$	50,479	$	40,150	$	206,159

During the third quarter of 2016, we made a decision to divest our Texas heavy civil business unit, a division of Primoris Heavy Civil within the Civil segment. We engaged a financial advisor to assist in the marketing and sale of the business unit, and planned to continue operating the business unit until completion of a sale. In April 2017, the Board of Directors determined that based on the information available, we would attain the best long-term value by withdrawing from the sales process and continuing to operate the business unit. We will aggressively pursue claims for five Texas Department of Transportation projects that resulted in significant losses recorded in 2016. However, there can be no assurance as to the final amounts collected. In accordance with ASC 350, "Intangibles—Goodwill and Other”, the planned divestiture triggered an analysis of the goodwill at Primoris Heavy Civil, resulting in a pre-tax, non-cash goodwill impairment charge of approximately $2.7 million in the third quarter of 2016.

There were no impairments of goodwill for the years ended December 31, 2018 and 2017.

The table below summarizes the intangible asset categories, amounts and the average amortization periods, which are generally on a straight-line basis (in thousands):


		December 31, 2018						December 31, 2017
	Weighted Average Life	Gross Carrying Amount		Accumulated Amortization		Intangible assets, net		Gross Carrying Amount		Accumulated Amortization		Intangible assets, net
Tradename	9 years	$	31,390	$	(25,156)	$	6,234	$	32,175	$	(22,238)	$	9,937
Customer relationships	16 years		97,400		(23,079)		74,321		49,900		(16,338)		33,562
Non-compete agreements	5 years		1,900		(1,387)		513		1,900		(820)		1,080
Other	3 years		275		(145)		130		275		(54)		221
Total	15 years	$	130,965	$	(49,767)	$	81,198	$	84,250	$	(39,450)	$	44,800

Amortization expense of intangible assets was $11.3 million, $8.7 million and $6.6 million for the years ended December 31, 2018, 2017 and 2016, respectively. In the second quarter of 2017, we recorded a $0.5 million impairment charge related to a tradename intangible asset in our Pipeline segment. The impairment charge is included in “Selling, general and administrative expenses” in the Consolidated Statements of Income. Estimated future amortization expense for intangible assets as of December 31, 2018 is as follows (in thousands):


	Estimated
	Intangible
	Amortization
For the Years Ending December 31,	Expense
2019	$	11,559
2020		8,814
2021		7,577
2022		6,416
2023		5,394
Thereafter		41,438
	$	81,198