9	ACQUIRED INTANGIBLE ASSETS, NET

Acquired intangible assets, net consisted of the following:

	At December 31,
	2012			2013
Cost:
Purchased software	$	6,803		$	9,647
Technology licenses		15,268			17,640
		22,071			27,287
Accumulated amortization:
Purchased software		(5,661	)		(7,054	)
Technology licenses		(5,591	)		(8,015	)
		(11,252	)		(15,069	)
IPR&D not subject to amortization		420			420
Less: Impairment loss in respect of IPR&D recognized		(420	)		(420	)
Acquired intangible assets, net	$	10,819		$	12,218

The intangible assets of the Group mainly consisted of purchased software which is used to support the business administration and the electronic design automation, and technology licenses acquired for the purpose of utilizing certain intellectual property held by third parties.

The Group has recorded amortization expense of $1,803, $3,056 and $3,480 for the years ended December 31, 2011, 2012 and 2013, respectively. Intangible asset amortization expense is estimated to be $4,897, $4,422, $3,869, $2,722 and $2,168 for the 2014, 2015, 2016, 2017 and 2018 fiscal years, respectively.

In 2011, the Group compared the IPR&D's carrying value to its respective fair value. The Group estimated the fair value of the IPR&D by the income approach. Significant assumptions inherent in the valuation methodologies for IPR&D are employed and include, but are not limited to, prospective financial information and discount rates. Based on this quantitative test, the Group determined that the fair value of the IPR&D tested in 2011 was lower than its carrying amount because the management decided to cease the entire research and development project of the application for Android, which is the primarily line of business of Mavrix reporting unit, due to of technological failure. Accordingly, the Group recognized an impairment loss of $ 420 on the IPR&D.