Accounts Receivable - Allowance for Doubtful Accounts Related to Accounts Receivable (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019		Jun. 30, 2018
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Allowance for doubtful accounts beginning of period	$ 59,963		$ 46,031
Provision for bad debts	40,142	[1]	26,495
Write-offs	(31,771)		(24,281)
Allowance for doubtful accounts end of period	$ 68,334		$ 48,245

[1] Reflects the impact of the Company's adoption of ASU 2016-02 "Leases", on January 1, 2019, using the modified retrospective transition method. Under this method, financial results reported in periods prior to 2019 are unchanged. Refer to footnote 2.