4. Long-Lived Assets

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


	March 31,		December 31,
	2017		2016
Property, plant and equipment cost	$	1,058,673	$	1,036,137
Less accumulated depreciation		459,875		440,140
	$	598,798	$	595,997

Depreciation expense amounted to $20.8 million and $21.4 million for the three months ended March 31, 2017 and 2016, respectively.

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


	March 31, 2017						December 31, 2016
	Gross				Net		Gross				Net
	Carrying		Accumulated		Carrying		Carrying		Accumulated		Carrying
	Value		Amortization		Value		Value		Amortization		Value
Subject to amortization:
Customer relationships	$	21,709	$	16,720	$	4,989	$	21,709	$	16,299	$	5,410
Trade name and other		320		306		14		320		302		18
		22,029		17,026		5,003		22,029		16,601		5,428
Not subject to amortization:
Brand name		27,300		—		27,300		27,300		—		27,300
		27,300		—		27,300		27,300		—		27,300
	$	49,329	$	17,026	$	32,303	$	49,329	$	16,601	$	32,728

As of March 31, 2017, the Company has goodwill of $12.1 million. Previously, $10.5 million of goodwill was recognized as part of the data center services segment and $1.6 million in the telecommunications segment. As further discussed in Note 14, because of recent operational, organizational and reporting changes, the Company has concluded it now has only one segment and one reporting unit. As such, the Company now classifies all goodwill in the one segment.

Amortization expense amounted to $0.4 million and $0.5 million for the three months ended March 31, 2017 and 2016, respectively. Estimated amortization expense for the next five years and thereafter is as follows (dollars in thousands):


Year ended December 31,
2017 (remaining months)	$	1,278
2018		1,307
2019		930
2020		574
2021		270
Thereafter		644
	$	5,003

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