Property and Equipment

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Property and equipment consisted of the following as of December 31, 2017 and 2016 (in thousands except years):



	December 31, 2017			December 31, 2016			Estimated Useful Life
Computer and networking equipment	$	1,292,587		$	1,170,471		3-7
Purchased software	61,276			51,727			3-10
Furniture and fixtures	48,521			41,968			5
Office equipment	26,949			24,497			3-5
Leasehold improvements	152,487			139,991			1-16
Internal-use software	765,162			656,053			2-7
Property and equipment, gross	2,346,982			2,084,707
Accumulated depreciation and amortization	(1,484,447		)	(1,283,690		)
Property and equipment, net	$	862,535		$	801,017

Depreciation and amortization expense on property and equipment and capitalized internal-use software for the years ended December 31, 2017, 2016 and 2015 was $341.4 million, $307.7 million and $272.5 million, respectively. During the years ended December 31, 2017, 2016 and 2015, the Company capitalized $28.9 million, $23.1 million and $17.9 million, respectively, of stock-based compensation related to employees who developed and enhanced internal-use software applications.

During the years ended December 31, 2017 and 2016, the Company wrote off $174.6 million and $93.4 million, respectively, of property and equipment, gross, along with the associated accumulated depreciation and amortization. The write-offs were primarily related to computer and networking equipment and internal-use software no longer in use. These assets had been substantially depreciated and amortized. In addition, during the year ended December 31, 2017, the Company wrote off $36.2 million of internal-use software as a result of certain restructuring efforts. These assets had a net book value of $32.0 million and are included in restructuring charges in the consolidated statements of income.