Business and Summary of Significant Accounting Policies - Accounts Receivable Provision (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounting Policies [Abstract]
Bad Debt Expense	$ 170,574	$ 128,333	$ 122,184
Provision for Returns and Uncollected Renewal Payments	32,815	39,590	40,927
Provision for Doubtful Accounts	$ 203,389	$ 167,923	$ 163,111