Patent Assets, Net

Patent assets, net, consisted of the following (in thousands):



	December 31, 2015			Additions			Disposals			June 30, 2016
Patent assets	$	824,258		$	37,160		$	(3,867	)	$	857,551
Accumulated amortization	(569,698		)	(79,430		)	3,822			(645,306		)
Patent assets, net	$	254,560								$	212,245

The Company’s acquired patent assets relate to technologies used or supplied by companies in a variety of market sectors, including consumer electronics, e-commerce, financial services, media distribution, mobile communications, networking, semiconductors and software. The Company amortizes each acquired patent asset portfolio on a straight-line basis over its estimated economic useful life. As of June 30, 2016, the estimated economic useful lives of the Company’s patent assets generally ranged from 24 to 60 months. As of June 30, 2016, the weighted-average estimated economic useful life at the time of acquisition of all patent assets acquired since the Company’s inception was 43 months.

As of June 30, 2016, the Company expects amortization expense in future periods to be as follows (in thousands):



2016 (remainder)	$	69,839
2017	89,922
2018	34,798
2019	14,674
2020	3,012
Total estimated future amortization expense	$	212,245

Amortization expense related to the Company's patent assets was $37.7 million and $35.1 million for the three months ended June 30, 2016 and 2015, respectively, and $79.5 million and $68.2 million for the six months ended June 30, 2016 and 2015, respectively.