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) - USD ($)
$ in Thousands
Sep. 30, 2015
Dec. 31, 2014
Derivative Assets    
Derivative Assets, Current $ 16,763 $ 27,850
Derivative Assets, Noncurrent 2,203  
Derivative Liabilities    
Derivative Liabilities, Current   (1,249)
Fair Value, Net Asset 18,966 26,601
Level 2 [Member]    
Derivative Assets    
Derivative Assets, Current 16,763 27,850
Derivative Assets, Noncurrent 2,203  
Derivative Liabilities    
Derivative Liabilities, Current   (1,249)
Fair Value, Net Asset $ 18,966 $ 26,601