5. Goodwill and Other Intangibles

Goodwill consists of the following as of September 30, 2018:


	(in thousands)
Balance at December 31, 2017	$	23,844
Additions for acquisitions		6,250
Divestiture adjustment		(135	)
Effects of currency exchange		(155	)

Balance at September 30, 2018	$	29,804

Other intangible assets consist of the following:


	September 30, 2018						December 31, 2017
	Gross Carrying Value		Accumulated Amortization		Net Carrying Value		Gross Carrying Value		Accumulated Amortization		Net Carrying Value
	(in thousands)
Product technology	$	10,143	$	5,483	$	4,660	$	10,267	$	4,908	$	5,359
Trademarks and licenses		3,465		1,530		1,935		1,948		1,468		480
Customer relationships		9,787		3,636		6,151		5,383		3,299		2,084
Other intangible assets		2,096		1,352		744		1,575		1,264		311

Total identifiable intangible assets	$	25,491	$	12,001	$	13,490	$	19,173	$	10,939	$	8,234

These intangible assets are being amortized over their useful lives ranging from 3 to 16 years. The weighted-average amortization period for these intangibles as of September 30, 2018 is 9.4 years. Amortization expense is included in general and administrative expense and was as follows for the periods indicated.


	Three months ended September 30,				Nine months ended September 30,
	2018		2017		2018		2017
	(in thousands)				(in thousands)
Amortization expense	$	380	$	443	$	1,213	$	1,353

We estimate that amortization expense for the remainder of 2018 and for each of the five succeeding fiscal years will be as follows:


	Year ended December 31,
	2018		2019		2020		2021		2022		2023
	(in thousands)
Amortization expense	$	521	$	1,972	$	1,721	$	1,523	$	1,316	$	1,257