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Derivative Financial Instruments (Commodity Contracts) (Details) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Commodity Contracts [Member]    
Derivative Instruments, Gain (Loss) [Line Items]    
Effective Portion of Cash Flow Hedges Recognized in Other Comprehensive Income (Loss) $ 2,610 $ 2,282