Quarterly report pursuant to Section 13 or 15(d)

Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details)

v3.7.0.1
Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - Not Designated as Hedging Instrument [Member] - USD ($)
$ in Thousands
Mar. 31, 2017
Dec. 31, 2016
Offsetting Assets and Liabilities [Line Items]    
Derivative Assets $ 6,032 $ 103
Derivative Liabilities (6,430) (18,296)
Current assets - Fair value of derivatives [Member]    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 5,055 1,836
Derivative asset, fair value, gross liability (1,962) (1,733)
Derivative Assets 3,093 103
Long-term assets: Fair value of derivatives [Member]    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 2,939  
Derivative Assets 2,939  
Current liabilities - Fair value of derivatives [Member]    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (8,392) (20,001)
Derivative liability, fair value, gross asset 1,962 1,733
Derivative Liabilities $ (6,430) (18,268)
Non-current liabilities - Fair value of derivatives [Member]    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability   (28)
Derivative Liabilities   $ (28)