INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2016

4.INTANGIBLE ASSETS

Intangible assets on the Company’s consolidated balance sheets consist of the following (in thousands):

		December 31, 2016							December 31, 2015
	Life	Gross Amount		Accumulated amortization			Net Book Value		Gross Amount		Accumulated amortization			Net Book Value
Customer lists	8 - 17 years	$	37,868	$	(10,087	)	$	27,781	$	34,149	$	(7,785	)	$	26,364
Trade name	10 - 12 years	6,038		(2,281		)	3,757		4,775		(1,793		)	2,982
Design and technologies	10 - 12 years	4,537		(1,840		)	2,697		2,189		(1,570		)	619
Patents	17 years	24		(7		)	17		24		(5		)	19
Total		$	48,467	$	(14,215	)	$	34,252	$	41,137	$	(11,153	)	$	29,984

Intangible assets acquired from the Heidrive acquisition were approximately $7,710 (Note 2). The weighted average amortization period for the acquired intangibles is 14.5 years.

Total amortization expense for intangible assets for the years 2016, 2015 and 2014 was $3,204, $2,644 and $2,714, respectively.

Estimated amortization expense for intangible assets is as follows:

Year ending December 31,	Total
2017	$	3,162
2018	3,162
2019	3,162
2020	3,162
2021	2,929
Thereafter	18,675
	$	34,252