Debt - (Summary of Debt) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Outstanding Principal	$ 2,396,214
Deferred financing costs	(6,854)	$ (2,267)
Total debt	2,412,200	2,423,698
Debt classified as current (included in other current liabilities)	(901,856)	(900,759)
Total long-term debt	1,510,344	1,522,939
Margin Loan Facility
Debt Instrument [Line Items]
Outstanding Principal	900,000
Carrying Value	900,000	900,000
Senior notes
Debt Instrument [Line Items]
Outstanding Principal	775,000
Carrying Value	797,840	803,287
Senior credit facility
Debt Instrument [Line Items]
Outstanding Principal	713,895
Carrying Value	713,895	715,124
Wells Fargo note payable
Debt Instrument [Line Items]
Outstanding Principal	7,319
Carrying Value	$ 7,319	$ 7,554

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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