4. Long-Lived Assets

Property, plant and equipment consisted of the following (dollars in thousands):


	September 30,		December 31,
	2015		2014
Property, plant and equipment	$	910,799	$	843,589
Less accumulated depreciation		(338,557)		(277,633)
	$	572,242	$	565,956

Depreciation expense amounted to $22.0 million and $63.9 million for the three and nine months ended September 30, 2015, respectively. Depreciation expense amounted to $19.0 million and $55.1 million for the three and nine months ended September 30, 2014, respectively.

The gross carrying amount and accumulated amortization of identifiable intangible assets are as follows (dollars in thousands):


	September 30, 2015						December 31, 2014
	Gross				Net		Gross				Net
	Carrying		Accumulated		Carrying		Carrying		Accumulated		Carrying
	Value		Amortization		Value		Value		Amortization		Value
Subject to amortization:
Customer relationships	$	21,709	$	13,628	$	8,081	$	21,709	$	11,799	$	9,910
Trade name and other		320		247		73		320		202		118
		22,029		13,875		8,154		22,029		12,001		10,028
Not subject to amortization:
Brand name		27,300		—		27,300		27,300		—		27,300
		27,300		—		27,300		27,300		—		27,300
	$	49,329	$	13,875	$	35,454	$	49,329	$	12,001	$	37,328

Amortization expense amounted to $0.6 million and $1.9 million for the three and nine months ended September 30, 2015, respectively. Amortization expense amounted to $0.7 million and $2.2 million for the three and nine months ended September 30, 2014, respectively. Estimated amortization expense for the next five years and thereafter is as follows (dollars in thousands):


2015 (remaining months)	$	624
2016		2,101
2017		1,703
2018		1,308
2019		930
Thereafter		1,488
	$	8,154