Property and Equipment

12 Months Ended

Dec. 31, 2018

Property, Plant and Equipment [Abstract]

Property and equipment consisted of the following as of December 31, 2018 and 2017 (in thousands except years):



	December 31, 2018			December 31, 2017			Estimated Useful Life
Computer and networking equipment	$	1,301,604		$	1,292,587		3-7
Purchased software	73,888			61,276			3-10
Furniture and fixtures	54,057			48,521			1-7
Office equipment	29,309			26,949			3-5
Leasehold improvements	184,700			152,487			1-15
Internal-use software	944,279			765,162			2-7
Property and equipment, gross	2,587,837			2,346,982
Accumulated depreciation and amortization	(1,677,219		)	(1,484,447		)
Property and equipment, net	$	910,618		$	862,535

Depreciation and amortization expense on property and equipment and capitalized internal-use software for the years ended December 31, 2018, 2017 and 2016 was $401.2 million, $341.4 million and $307.7 million, respectively. During the years ended December 31, 2018, 2017 and 2016, the Company capitalized $34.8 million, $28.9 million and $23.1 million, respectively, of stock-based compensation related to employees who developed and enhanced internal-use software applications.

During the years ended December 31, 2018 and 2017, the Company wrote off $208.0 million and $174.6 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, 2018, the Company wrote off $4.9 million of internal-use software and a purchased software license as a result of certain restructuring efforts. 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 the net charge from these write offs are included in restructuring charges in the consolidated statements of income.