Intangible Assets

12 Months Ended

Dec. 31, 2014

The following tables summarize the Company’s total purchased intangible assets (in thousands):



	Gross		Accumulated Amortization			Net
December 31, 2014
Purchased technology	$	114,754	$	(87,398	)	$	27,356
Patents	6,472		(6,472		)	—
Customer lists	37,000		(26,284		)	10,716
Trade names	11,536		(6,384		)	5,152
Backlog	2,127		(2,127		)	—
Total intangible assets	$	171,889	$	(128,665	)	$	43,224
December 31, 2013
Purchased technology	$	114,754	$	(79,189	)	$	35,565
Patents	6,472		(6,472		)	—
Customer lists	37,000		(21,997		)	15,003
Trade names	11,536		(5,594		)	5,942
Backlog	2,127		(2,127		)	—
Total intangible assets	$	171,889	$	(115,379	)	$	56,510

Intangible assets amortization expense was $13.3 million, $13.8 million and $14.8 million for the years ended December 31, 2014, 2013 and 2012. The Company’s purchased intangible assets have remaining useful lives of one to seven years as of December 31, 2014. The Company reviews for impairment all of its purchased intangible assets whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable.

The estimated future amortization expense of purchased intangible assets as of December 31, 2014 is as follows (in thousands):



For the Years Ending December 31,	Estimated Intangible Amortization Amount
2015	$	12,901
2016	12,747
2017	10,714
2018	4,870
2019	790
Thereafter	1,202
Total estimated future amortization expense	$	43,224