Note 10—Goodwill and Intangible Assets

During the years ended December 31, 2018 and 2017, the change in the carrying amount of goodwill was as follows (in thousands):



Balance at January 1, 2017	$	105,732
Wyoming Refining acquisition purchase price allocation adjustment (1)	1,455
Balance at December 31, 2017	107,187
Acquisition of Northwest Retail (1)	46,210
Balance at December 31, 2018	$	153,397

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(1)	Please read Note 4—Acquisitions for further discussion.

Intangible assets consist of the following (in thousands):



	December 31,
	2018			2017
Intangible assets:
Railcar leases	$	3,249		$	3,249
Trade names and trademarks	6,267			6,267
Customer relationships	32,064			32,064
Total intangible assets	41,580			41,580
Accumulated amortization:
Railcar leases	(3,249		)	(3,249		)
Trade name and trademarks	(5,037		)	(4,951		)
Customer relationships	(9,347		)	(6,776		)
Total accumulated amortization	(17,633		)	(14,976		)
Net:
Railcar leases	—			—
Trade name and trademarks	1,230			1,316
Customer relationships	22,717			25,288
Total intangible assets, net	$	23,947		$	26,604

Amortization expense was approximately $2.7 million, $3.3 million, and $4.5 million for the years ended December 31, 2018, 2017, and 2016, respectively. Our intangible assets related to customer relationships and trade names have an average useful life of 13.5 years. Expected amortization expense for each of the next five years and thereafter is as follows (in thousands):



Year Ended	Amount
2019	$	2,658
2020	2,658
2021	2,658
2022	2,658
2023	2,658
Thereafter	10,657
	$	23,947