Business and Summary of Significant Accounting Policies - Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Beginning Balance	$ 35,690	$ 34,861	$ 27,401
Accounts Written Off, net of Recoveries	(192,133)	(167,094)	(155,651)
Accounts Receivable Provision	203,389	167,923	163,111
Ending Balance	$ 46,946	$ 35,690	$ 34,861