Intangible Assets

The following is a summary of intangible assets:



		Years Ended September 30,
		2017							2016
	Useful Life	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
		(dollars in thousands)
Customer lists	6-10 years	$	2,471	$	(1,521	)	$	950	$	2,432	$	(1,164	)	$	1,268
Technology	5-10 years	3,386		(2,024		)	1,362		3,214		(1,678		)	1,536
Trade names	10-15 Years	1,468		(285		)	1,183		1,455		(219		)	1,236
Other	2-10 years	78		(78		)	—		277		(217		)	60
		$	7,403	$	(3,908	)	$	3,495	$	7,378	$	(3,278	)	$	4,100

Amortization expense related to intangible assets was $0.8 million, $0.8 million and $1.2 million in 2017, 2016 and 2015, respectively. The aggregate amortization expense for the intangible assets for each of the five succeeding fiscal years is estimated to be $0.6 million, $0.6 million, $0.6 million, $0.4 million, $0.3 million and $1.2 million in 2018, 2019, 2020, 2021, 2022 and thereafter, respectively.

On December 24, 2014, we acquired a 51% controlling interest in SoLayTec. The intangible assets of SoLayTec total $2.1 million, of which $1.9 million is included in “Technology” and $0.2 million is included in “Trade names” in the table above. On January 30, 2015, we completed the merger with BTU. The intangible assets of BTU total $2.9 million, of which $1.2 million is included in “Trade names” and $1.7 million is included in “Customer lists” in the table above. See Note 12, “Acquisitions,” for more information regarding the acquisition of SoLayTec and the merger with BTU.

As a result of the sale of our partial ownership in Kingstone in 2015, we derecognized $3.2 million of intangible assets and $1.9 million of accumulated amortization. See Note 13, “Deconsolidation,” for additional details.