Basis and Summary of Significant Accounting Policies - Components of the Accounts Receivable Provision (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Accounting Policies [Abstract]
Bad Debt Expense	$ 96,651	$ 68,044
Provision for Returns and Uncollected Renewal Payments	16,426	14,062
Accounts Receivable Provision	$ 113,077	$ 82,106