Intangible Assets, net

The following table summarizes the Company’s intangible assets as of September 30, 2019 and December 31, 2018:



	Estimated Useful Life (Years)	Gross Carrying Amount at December 31, 2018		Gross Impairment		Accumulated Amortization		Net Book Value at September 30, 2019
Developed technology	13	$	18,800	$	8,500	$	1,056	$	9,244
Customer relationships	1	270		—		270		—
		$	19,070	$	8,500	$	1,326	$	9,244

The Company uses the straight-line method to determine the amortization expense for its definite lived intangible assets. The weighted-average remaining useful life for the intangible assets is 11.7 years. Amortization expense related to the purchased intangible assets was $362 and $289 for the three months ended September 30, 2019 and 2018, respectively, and $1,199 and $572 for the nine months ended September 30, 2019 and 2018, respectively. The Company recorded an impairment charge of $7,628 related to specific developed technology allocated to the Quickload for the three months ended September 30, 2019. Amortizable intangible assets are evaluated for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets may not be recoverable through the estimated undiscounted future cash flows derived from such assets. The Company is developing and testing a new transload technology and no longer plans to actively market the Quickload system and as such, all developed technology intangible assets related to the Quickload have been impaired as of September 30, 2019.

The table below reflects the future estimated amortization expense for amortizable intangible assets as of September 30, 2019.




Remainder of 2019	$	264
2020	792
2021	792
2022	792
2023	792
Thereafter	5,812
Total	$	9,244