2.	Intangible and Other Assets

Following is a summary of intangible assets as of December 31:

		2017				2016
	Weighted Average Life	Gross Amount		Accumulated Amortization		Gross Amount		Accumulated Amortization
Intangibles:
Patents and licenses, software and hardware designs	6 years	$	5,320	$	3,540	$	5,033	$	3,187
Developed technology	10 years		2,782		2,295		2,782		2,017
Customer relationships and non-compete	9 years		2,838		2,621		2,838		2,331
		$	10,940	$	8,456	$	10,653	$	7,535

Amortization expense for 2017, 2016 and 2015 was $921, $915 and $1,235, respectively. Estimated amortization expense for each of the ensuing years through December 31, 2022 is $889, $602, $341, $323 and $40, respectively.

Following is a summary of other assets as of December 31:

	2017		2016
Other assets:
Bauxite raw materials:
Inventories	$	3,527	$	3,989
Other assets		5,434		1,524
	$	8,961	$	5,513

Bauxite raw materials are used in the production of heavyweight ceramic products. As of December 31, 2017 and 2016, the Company has classified as long-term assets those bauxite raw materials inventories that are not expected to be consumed in production during the upcoming twelve month period. For additional information, refer to Note 4 – Impairment of Long-Lived Assets. Other assets as of December 31, 2017 includes a $4,000 receivable relating to additional money owed us relating to the sale of our Russian proppant business. For additional information, refer to Note 17 – Sale of Russian Proppant Business.