Annual report pursuant to Section 13 and 15(d)

Derivative Instruments And Hedging Strategies (Recognized Gains (Losses) On Derivative Instruments Not Designated As Hedging Instruments) (Details)

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Derivative Instruments And Hedging Strategies (Recognized Gains (Losses) On Derivative Instruments Not Designated As Hedging Instruments) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Derivative [Line Items]      
Derivative gains (losses), net $ 19,727 $ (14,131) $ 1,921
Equity Option [Member]      
Derivative [Line Items]      
Derivative gains (losses), net 0 0 (452)
Foreign Exchange Forward [Member]      
Derivative [Line Items]      
Derivative gains (losses), net 291 (296) (519)
Three Point Seven Five Percentage Convertible Notes [Member]      
Derivative [Line Items]      
Embedded Derivative, Loss on Embedded Derivative   (13,826)  
Embedded Derivative, Gain on Embedded Derivative 19,436   2,900
Exchange Traded [Member] | Commodity Contract [Member]      
Derivative [Line Items]      
Derivative gains (losses), net 0 (9) (1,493)
Other Trading [Member] | Commodity Contract [Member]      
Derivative [Line Items]      
Derivative gains (losses), net $ 0 $ 0 $ 1,485