Goodwill represents the excess of the purchase price over the net amount of identifiable assets acquired and liabilities assumed in a business combination measured at fair value. The Company evaluates goodwill for impairment annually on October 1 of each year and upon the occurrence of triggering events or substantive changes in circumstances that could indicate a potential impairment by assessing qualitative factors or performing a quantitative analysis in determining whether it is more likely than not that the fair value of the net assets is below their carrying amounts.

No impairment charges relating to goodwill were recorded in the years ended December 31, 2018, 2017 and 2016.

The following table presents the balances of goodwill as of December 31, 2018 and 2017 (in thousands).

Intangible assets acquired in a business combination are recognized separately from goodwill and are initially recognized at their fair value at the acquisition date. Intangible assets acquired include intellectual property (product design), customer relationships, and trade names. These are definite-lived assets and are amortized on a straight-line basis over their useful lives. Intangible assets are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets might not be recoverable. Conditions that would necessitate an impairment assessment include a significant decline in the observable market value of an asset, a significant change in the extent or manner in which an asset is used, or any other significant adverse change that would indicate that the carrying amount of an asset or group of assets may not be recoverable. No impairment charges relating to intangible assets were recorded in the years ended December 31, 2018, 2017 and 2016.

The following table provides the details of identified intangible assets, by major class, for the periods indicated (in thousands):

		December 31, 2018							December 31, 2017
	Estimated Useful Life (Years)	Gross Carrying Amount		Accumulated Amortization			Intangible Assets, Net		Gross Carrying Amount		Accumulated Amortization			Intangible Assets, Net
Intangible assets subject to amortization:
Intellectual property	20	$	114,411	$	(18,115	)	$	96,296	$	114,411	$	(12,395	)	$	102,016
Trade names	10 - 20		83,358		(13,182	)		70,176		83,468		(9,375	)		74,093
Customer relationships	10 - 20		68,891		(11,053	)		57,838		68,060		(7,268	)		60,792
Licensor relationships	10 - 20		11,122		(1,790	)		9,332		13,908		(341	)		13,567
Supplier relationships	2		304		(301	)		3		322		(141	)		181
Total		$	278,086	$	(44,441	)	$	233,645	$	280,169	$	(29,520	)	$	250,649

Amortization expense for the years ended December 31, 2018, 2017 and 2016 was $15.0 million, $14.4 million, and $12.9 million, respectively. The future five-year amortization of intangibles subject to amortization at December 31, 2018 was as follows (in thousands):