PROPERTY AND EQUIPMENT

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

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



	December 31,
	2018			2017
Network equipment	$	274,322		$	247,190
Network equipment under capital lease	14,206			14,206
Furniture and equipment	28,583			26,246
Software	66,924			43,930
Leasehold improvements	414,212			412,631
Buildings under capital lease	269,455			227,482
Property and equipment, gross	1,067,701			971,685
Less: accumulated depreciation and amortization ($55,198 and $50,253 related to capital leases at December 31, 2018 and 2017, respectively)	(589,640		)	(513,120		)
	$	478,061		$	458,565

During the year ended December 31, 2018, we disposed or retired $4.4 million of property and equipment with accumulated depreciation of $4.2 million during the year ended December 31, 2018. We disposed or retired $9.2 million of assets with accumulated depreciation of $7.3 million during the year ended December 31, 2017 and $5.0 million of assets with accumulated depreciation of $4.4 million during the year ended December 31, 2016.

During the year ended December 31, 2018, there were no impairments in leasehold improvements. During the year ended December 31, 2017, we determined that we would not use certain leasehold improvements from our recently exited data center property and recorded an impairment of $0.5 million. At the time of disposal, the leasehold improvements had a cost of $22.4 million with accumulated depreciation of $21.9 million.

Depreciation and amortization of property and equipment consisted of the following (in thousands):



	Year ended December 31,
	2018		2017		2016
Costs of sales and services	$	75,998	$	70,368	$	71,626
Other depreciation and amortization	10,644		2,478		2,274
Subtotal	86,642		72,846		73,900
Amortization of acquired and developed technologies	4,034		2,147		3,048
Total depreciation and amortization	$	90,676	$	74,993	$	76,948