Intangible Assets

12 Months Ended

Dec. 31, 2015

Intangible assets are summarized as follows (in thousands):



	Weighted Average Estimated Useful Life	December 31,
	Weighted Average Estimated Useful Life	2015			2014
Product technology	10 years	$	76,182		$	67,620
Customer relationships	12 years	69,272			80,206
Trademarks and trade name portfolios	14 years	7,540			7,160
Trade name portfolio not subject to amortization	Indefinite	37,673			38,317
In-process research and development	n/a	2,250			550
Other	8 years	1,474			21,012
Acquired identifiable intangibles		194,391			214,865
Less accumulated amortization		(58,173		)	(87,997		)
Net acquired identifiable intangibles		136,218			126,868
Patents	7 years	6,104			9,905
Less accumulated amortization		(1,671		)	(4,544		)
Net patents		4,433			5,361
Acquired in-place leases and other	7 years	2,080			9,309
Less accumulated amortization		(1,429		)	(8,326		)
Net acquired in-place leases and other		651			983
		$	141,302		$	133,212

Note 8. Intangible Assets - (Continued)

Intangible assets are summarized as follows (in thousands):

During the year ended December 31, 2015, the Company acquired $27.4 million of identifiable intangible assets as part of the acquisition of DVTEL, as described in Note 18, "Business Acquisitions." During the year ended December 31, 2014, the Company purchased certain patents for $5.8 million.

The aggregate amortization expense recorded in 2015, 2014 and 2013 was $16.4 million, $21.1 million and $24.7 million, respectively. For intangible assets recorded at December 31, 2015, the estimated future aggregate amortization expense for the years ending December 31, 2016 through 2020 is approximately (in thousands):



2016	$	15,708
2017	14,964
2018	13,129
2019	12,375
2020	10,682