Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details)

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Fair Value Measurements (Fair Value of Assets and Liabilities Measured on Recurring Basis) (Details) - Fair Value, Measurements, Recurring [Member] - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Derivative Assets    
Derivative Asset $ 6,032 $ 103
Derivative Liabilities    
Derivative Liabilities (6,430) (18,296)
Total net liabilities (398) (18,193)
Level 2 [Member]    
Derivative Assets    
Derivative Asset 6,032 103
Derivative Liabilities    
Derivative Liabilities (6,430) (18,296)
Total net liabilities $ (398) $ (18,193)