Acacia’s only identifiable intangible assets are patents and patent rights, with estimated remaining economic useful lives ranging from one to nine years. For all periods presented, all of Acacia’s identifiable intangible assets were subject to amortization. The gross carrying amounts and accumulated amortization related to investments in intangible assets as of December 31, 2014 and 2013 are as follows (in thousands):



	2014			2013

Gross carrying amount - patents	$	453,201		$	400,755
Accumulated amortization - patents	(166,565		)	(112,323		)
Patents, net	$	286,636		$	288,432

The weighted-average remaining estimated economic useful life of Acacia’s patents and patent rights is 6 years. Scheduled annual aggregate amortization expense is estimated to be $52,019,000 in 2015, $49,332,000 in 2016, $48,245,000 in 2017, $44,117,000 in 2018, $38,679,000 in 2019 and $54,244,000 thereafter.

For the years ended December 31, 2014, 2013 and 2012, Acacia paid patent investment costs totaling $42,746,000, $25,061,000 and $178,260,000 (excluding the investment in ADAPTIX), respectively. The patents have estimated economic useful lives ranging from three to ten years. Included in net additions to capitalized patent costs during the years ended December 31, 2014 and 2013 are accrued patent investment costs totaling $16,700,000 and $4,000,000, respectively, which are amortized over the estimated economic useful life of the related patents.

Refer to Note 7 to these consolidated financial statements for additions to patents and goodwill in connection with Acacia’s acquisition of ADAPTIX and the related application of the acquisition method of accounting.

During the periods presented, certain operating subsidiaries recovered up-front patent portfolio advances from applicable net licensing proceeds prior to the scheduled amortization of such up-front patent portfolio advances, resulting in the acceleration of amortization expense for the applicable patent-related assets. For the years ended December 31, 2014, 2013 and 2012, accelerated amortization expense related to the recovery of up-front patent portfolio advances totaled $1,247,000, $592,000 and $10,574,000, respectively.

For the years ended December 31, 2014, 2013 and 2012, pursuant to the terms of the respective inventor agreements, certain Acacia operating subsidiaries elected to terminate or sell their rights to patent portfolios, resulting in the acceleration of amortization expense for the patent-related assets totaling $2,702,000, $1,747,000 and $3,034,000, respectively. Included in amortization of patents for the year ended December 31, 2014 and 2013 are patent impairment charges totaling $3,497,000 and $4,619,000, respectfully. There was no impairment charge in 2012. The impairment charges related to partial impairment of a portfolio due to a reduction in expected estimated future net cash flows (2014 only) and certain patent portfolios that management determined it would no longer allocate future resources to in connection with the licensing and enforcement of such portfolios, due primarily to potential prior art related complexities in two of the programs (2013 only) and/or the overall determination that future resources would be allocated to other licensing and enforcement programs with higher potential return profiles. The impairment charges consisted of the excess of the asset’s carrying value over its estimated fair value as of December 31, 2014 and 2013.

For the years ended December 31, 2014, 2013 and 2012, capitalized patent costs and accumulated amortization, and sales proceeds and other costs, related to patent-related sales and disposals are as follows (in thousands):



	2014		2013		2012

Capitalized patent costs	$	3,000	$	3,500	$	5,500
Accumulated amortization	298		1,753		2,466
Sales proceeds	3,500		1,000		2,792