Revenue (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Revenue from Contract with Customer [Abstract]
Accounts Receivable, Less Allowance	$ 2,625,066	$ 2,104,555	$ 2,377,874
Contract Assets (Current)	45,678	33,031
Contract Assets (Long-Term)	130,805	135,150
Contract Liabilities (Current)	180,369	208,909
Contract Liabilities (Long-Term)	$ 8,745	$ 8,745

Amount due from customers or clients, within one year of the balance sheet date (or the normal operating cycle, whichever is longer), for goods or services (including trade receivables) that have been delivered or sold in the normal course of business, reduced to the estimated net realizable fair value by an allowance established by the entity of the amount it deems uncertain of collection.

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Amount, after allowance for credit loss, of right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time, classified as current.

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Amount of obligation to transfer good or service to customer for which consideration has been received or is receivable, classified as current.

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