Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

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Amount before accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Amount after accumulated depreciation, depletion and amortization of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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Property and Equipment, net (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Property and equipment, net
Property and equipment, gross	$ 699,117		$ 699,117		$ 545,267
Less accumulated depreciation and amortization	(230,695)		(230,695)		(184,126)
Property and equipment, net	468,422		468,422		361,141
Depreciation and amortization	28,600	$ 19,000	54,300	$ 39,100
Furniture and computer equipment
Property and equipment, net
Property and equipment, gross	263,436		263,436		213,790
Site and software development costs
Property and equipment, net
Property and equipment, gross	143,376		143,376		118,356
Leasehold improvements
Property and equipment, net
Property and equipment, gross	87,055		87,055		82,614
Construction in progress
Property and equipment, net
Property and equipment, gross	63,586		63,586		46,826
Buildings
Property and equipment, net
Property and equipment, gross	$ 141,664		$ 141,664		$ 83,681