Long-Term Debt (Schedule of Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Discount	$ (10,500)	$ (13,900)
Total Long-term Debt	1,296,500	1,282,800
Less current maturities	(23,241)	(12,965)
Long-term debt, less current maturities	$ 1,273,287	$ 1,269,849
Series 2014-1 4.277% Fixed Rate Senior Secured Notes, Class A-2
Debt Instrument [Line Items]
Debt interest rate (percent)	4.277%	4.277%
Senior Notes due October 2018, at a fixed rate of 9.5%	$ 1,287,000	$ 1,296,800
Series 2014-1 Variable Funding Senior Notes Class A-1, At A Variable Interest Rate Of 4.5245%
Debt Instrument [Line Items]
Debt interest rate (percent)	4.403%
Senior Notes due October 2018, at a fixed rate of 9.5%	$ 20,000	$ 0