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 amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

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Summary of Significant Accounting Policies - Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment
Depreciation expense	$ 80,900	$ 76,500	$ 75,300
Property and equipment, gross	799,303	753,747
Accumulated depreciation	(648,555)	(595,109)
Property and equipment, net	150,748	158,638
Building improvements
Property and Equipment
Property and equipment, gross	$ 18,954	17,974
Building improvements \| Minimum
Property and Equipment
Estimated useful lives of assets	2 years
Building improvements \| Maximum
Property and Equipment
Estimated useful lives of assets	10 years
Equipment
Property and Equipment
Property and equipment, gross	$ 201,343	204,632
Equipment \| Minimum
Property and Equipment
Estimated useful lives of assets	3 years
Equipment \| Maximum
Property and Equipment
Estimated useful lives of assets	15 years
Capital leases - property
Property and Equipment
Property and equipment, gross	$ 26,945	26,945
Capital leases - equipment
Property and Equipment
Property and equipment, gross	24,932	18,183
Capitalized internal-use software
Property and Equipment
Depreciation expense	50,000	49,500	$ 47,600
Property and equipment, gross	527,129	486,013
Property and equipment, net	$ 71,700	$ 79,600
Capitalized internal-use software \| Minimum
Property and Equipment
Estimated useful lives of assets	3 years
Capitalized internal-use software \| Maximum
Property and Equipment
Estimated useful lives of assets	5 years