Basis of Presentation and Significant Accounting Policies Accounts Receivable Allowance Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Accounts receivable allowance balance, beginning of the period	$ 12,504	$ 5,543	$ 6,795
Additions charged to revenues, costs and expenses	14,786	14,009	5,277
Deductions	(22,476)	(7,048)	(6,529)
Accounts receivable allowance balance, end of the period	$ 4,814	$ 12,504	$ 5,543