Quarterly report pursuant to Section 13 or 15(d)

Debt (Summary of Debt) (Details)

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Debt (Summary of Debt) (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Debt Instrument [Line Items]    
Outstanding Principal $ 2,874,196  
Deferred financing costs (1,965) $ (2,267)
Total debt 2,943,464 2,886,034
Debt classified as current (included in other current liabilities) (901,306) (900,759)
Total long-term debt 2,042,158 1,985,275
Margin Loan Facility    
Debt Instrument [Line Items]    
Outstanding Principal 900,000  
Carrying Value 900,000 900,000
Exchangeable senior debentures    
Debt Instrument [Line Items]    
Outstanding Principal 477,250  
Carrying Value 521,376 462,336
Senior notes    
Debt Instrument [Line Items]    
Outstanding Principal 775,000  
Carrying Value 802,107 803,287
Senior credit facility    
Debt Instrument [Line Items]    
Outstanding Principal 714,510  
Carrying Value 714,510 715,124
Wells Fargo note payable    
Debt Instrument [Line Items]    
Outstanding Principal 7,436  
Carrying Value $ 7,436 $ 7,554