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Debt And Interest Expense (Components Of Interest Expense) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Short-term Debt [Line Items]      
Contractual interest on Convertible Debentures $ 47,432 $ 40,625 $ 40,625
Interest Expense, Debt 73,638 60,938 54,667
Amortization of debt discount on the Convertible Debentures 12,012 11,094 10,218
Other interest expense 3,254 2,907 2,121
Total interest expense $ 136,336 $ 115,564 $ 107,631