Intangible Assets

12 Months Ended

Dec. 31, 2015

Intangible Assets.

Intangible Assets

8. Intangible Assets

        Intangible assets, consisting of acquired technology, customer relationships and trademarks, are amortized using the straight-line method over their useful lives of five to ten years.

        The gross carrying amount and accumulated amortization of the Company's acquired identifiable intangible assets as of December 31, 2015 are as follows (in thousands):

	Weighted Average Amortization Period	Gross Carrying Amount		Accumulated Amortization			Total
Acquired technology	9 years	$	4,793	$	(403	)	$	4,390
Customer relationships	10 years		260		(45	)		215
Trademark	5 years		60		(21	)		39
		$	5,113	$	(469	)	$	4,644

        The gross carrying amount and accumulated amortization of the Company's acquired identifiable intangible assets as of December 31, 2014 are as follows (in thousands):

	Weighted Average Amortization Period	Gross Carrying Amount		Accumulated Amortization			Total
Acquired technology	8 years	$	17,697	$	(16,540	)	$	1,157
Customer relationships	8 years		1,260		(978	)		282
Trademark	5 years		60		(9	)		51
		$	19,017	$	(17,527	)	$	1,490

        The change in the gross carrying amount of the acquired technology from December 31, 2014 to December 31, 2015 is due to the acquisition of HyPulsion, and changes attributed to foreign currency translation, offset by removal of assets that became fully amortized.

        Amortization expense for acquired identifiable intangible assets for the years ended December 31, 2015, 2014, and 2013 was $1.0 million, $2.4 million, and $2.3 million, respectively. Estimated amortization expense for subsequent years is as follows (in thousands):

2016	583
2017	583
2018	583
2019	475
2020	439
Thereafter	1,981
Total	4,644