Long-Term Debt (Schedule of Debt) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Class A-2-I and A-2-II (2019) and Class A-2 (2018) Note debt issuance costs	$ (12,800)	$ (9,700)
Long-term debt, net of debt issuance costs	1,287,200	1,299,100
Current portion of long-term debt	0	(25,000)
Long-term debt, less current maturities	$ 1,287,227	$ 1,274,087
Series 2019-1 4.194% Fixed Rate Senior Secured Notes, Class A-2-I
Debt Instrument [Line Items]
Debt interest rate (percent)	4.194%	4.194%
Senior notes	$ 700,000	$ 0
Series 2019-1 4.723% Fixed Rate Senior Secured Notes, Class A-2-II
Debt Instrument [Line Items]
Debt interest rate (percent)	4.723%	4.723%
Senior notes	$ 600,000	$ 0
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	$ 0	$ 1,283,800
Series 2019-1 Variable Funding Senior Notes Class A-1, variable interest rate of ___% at June 30, 2019
Debt Instrument [Line Items]
Class A-2-I and A-2-II (2019) and Class A-2 (2018) Note debt issuance costs	(3,000)
Series 2018-1 Variable Funding Senior Notes Class A-1, variable interest rate of 4.93% at December 31, 2018
Debt Instrument [Line Items]
Debt interest rate (percent)		4.93%
Senior notes	0	$ 25,000
Class A-2-I and A-2-II (2019) and Class A-2 (2018) Note debt issuance costs	$ (2,800)

Contractual interest rate for funds borrowed, under the debt agreement.

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