Accounts Receivable - Allowance for Doubtful Accounts Related to Accounts Receivable (Details) - USD ($) $ in Thousands		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for doubtful accounts beginning of period		$ 46,031	$ 32,506
Provision for bad debts	[1]	26,495	27,648
Write-offs		(24,281)	(12,318)
Allowance for doubtful accounts end of period		$ 48,245	$ 47,836

[1] Reflects the impact of the Company's adoption of Accounting Standards Update 2016-18, "Statement of Cash Flows (Topic 230)", which was adopted by the Company on January 1, 2018 and applied retrospectively to results for 2017. The adoption of Topic 230 resulted in the statement of cash flows presenting the changes in the total of cash, cash equivalents and restricted cash. As a result, the Company will no longer present transfers between cash and cash equivalents and restricted cash in the statement of cash flows.