Patent Assets, Net

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



	December 31, 2013			Additions			Sales			December 31, 2014
Patent assets	$	529,526		$	136,468		$	(704	)	$	665,290
Accumulated amortization	(309,572		)	(119,694		)	325			(428,941		)
Patent assets, net	$	219,954								$	236,349



	December 31, 2012			Additions			Sales			December 31, 2013
Patent assets	$	403,875		$	126,501		$	(850	)	$	529,526
Accumulated amortization	(204,561		)	(105,533		)	522			(309,572		)
Patent assets, net	$	199,314								$	219,954

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 portfolio of patent assets on a straight-line basis over its estimated economic useful life. As of December 31, 2014, the estimated economic useful lives of the Company’s patent assets generally ranged from 24 to 60 months. As of December 31, 2014, the weighted-average estimated economic useful life at the time of acquisition was 45 months.

As of December 31, 2014, the Company expects amortization expense in future periods to be as follows (in thousands):



2015	$	111,415
2016	80,576
2017	36,241
2018	7,166
2019	951
Total estimated future amortization expense	$	236,349

Amortization expense was $119.7 million, $105.5 million and $80.4 million for the years ended December 31, 2014, 2013 and 2012, respectively.

Syndicated Acquisitions

Syndicated acquisitions are transactions involving patent assets that may cost more than the Company is prepared to spend with its own capital resources or that are relevant only to a very small number of clients. In such transactions, the Company may work to acquire these assets with financial assistance from the particular clients against whom they are being or may be asserted. Such clients either pay amounts separate from their subscription fee or, less frequently, lend the Company funds to be used in the transaction. As discussed in the revenue recognition policy in Note 2, the Company may treat the contributions from such clients as revenue on a gross or net basis depending on the specific facts and circumstances of the transaction. In the event that such contributions are recognized on a net basis, the Company will only capitalize the acquired asset that relates to its non-contributing clients. As a result, in such situations the cost basis of the acquired patent rights excludes the amounts paid by the contributing clients.