Property and Equipment

12 Months Ended

Dec. 31, 2016

Property, Plant and Equipment [Abstract]

Property and equipment consisted of the following as of December 31, 2016 and 2015 (dollars in thousands):



	December 31, 2016			December 31, 2015			Estimated Useful Life in Years
Computer and networking equipment	$	1,170,471		$	1,046,739		3-7
Purchased software	51,727			46,509			3-10
Furniture and fixtures	41,968			35,212			5
Office equipment	24,497			21,108			3-5
Leasehold improvements	139,991			119,466			1-16
Internal-use software	656,053			546,520			2-7
Property and equipment, gross	2,084,707			1,815,554
Accumulated depreciation and amortization	(1,283,690		)	(1,062,374		)
Property and equipment, net	$	801,017		$	753,180

Depreciation and amortization expense on property and equipment and capitalized internal-use software for the years ended December 31, 2016, 2015 and 2014 was $307.7 million, $272.5 million and $215.3 million, respectively. During the years ended December 31, 2016, 2015 and 2014, the Company capitalized $23.1 million, $17.9 million and $15.2 million, respectively, of stock-based compensation related to employees who developed and enhanced internal-use software applications.

During the years ended December 31, 2016 and 2015, the Company wrote off $93.4 million and $48.7 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.