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) - Balance Sheet Location [Domain] - USD ($)
$ in Thousands
Jun. 30, 2015
Dec. 31, 2014
Derivative Assets    
Derivative Assets, Current $ 6,889 $ 27,850
Derivative Assets, Noncurrent 205  
Derivative Liabilities    
Derivative Liabilities, Current (1,622) (1,249)
Fair Value, Net Asset 5,472 26,601
Level 2 [Member]    
Derivative Assets    
Derivative Assets, Current 6,889 27,850
Derivative Assets, Noncurrent 205  
Derivative Liabilities    
Derivative Liabilities, Current (1,622) (1,249)
Fair Value, Net Asset $ 5,472 $ 26,601