Property and Equipment

12 Months Ended

Dec. 31, 2019

Property, Plant and Equipment [Abstract]

Property and equipment consisted of the following as of December 31, 2019 and 2018 (in thousands except years):



	December 31, 2019			December 31, 2018			Estimated Useful Life
Computer and networking equipment	$	1,469,293		$	1,301,604		3-7
Purchased software	90,450			73,888			3-10
Furniture and fixtures	65,683			54,057			1-7
Office equipment	38,178			29,309			3-5
Leasehold improvements	235,279			184,700			1-15
Internal-use software	1,132,180			944,279			2-7
Property and equipment, gross	3,031,063			2,587,837
Accumulated depreciation and amortization	(1,878,910		)	(1,677,219		)
Property and equipment, net	$	1,152,153		$	910,618

Depreciation and amortization expense on property and equipment and capitalized internal-use software for the years ended December 31, 2019, 2018 and 2017 was $402.1 million, $401.2 million and $341.4 million, respectively. During the years ended December 31, 2019, 2018 and 2017, the Company capitalized $35.9 million, $34.8 million and $28.9 million, respectively, of stock-based compensation related to employees who developed and enhanced internal-use software applications.

During the years ended December 31, 2019 and 2018, the Company wrote off $166.7 million and $208.0 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, the Company wrote off $3.8 million and $4.9 million, primarily of internal-use software as a result of certain restructuring efforts during the year ended December 31, 2019 and December 31, 2018, respectively.