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)

v3.10.0.1
Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - USD ($)
$ in Thousands
Jun. 30, 2018
Dec. 31, 2017
Offsetting Assets and Liabilities [Line Items]    
Derivative asset $ 2,299 $ 0
Not Designated as Hedging Instrument    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset 13,868 406
Derivative liability (47,084) (29,028)
Not Designated as Hedging Instrument | Current assets: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 33,530 406
Derivative asset, fair value, gross liability (21,961) 0
Derivative asset 11,569 406
Not Designated as Hedging Instrument | Long-term assets: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 7,536  
Derivative asset, fair value, gross liability (5,237)  
Derivative asset 2,299  
Not Designated as Hedging Instrument | Current liabilities: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (57,909) (27,744)
Derivative liability, fair value, gross asset 21,961 0
Derivative liability (35,948) (27,744)
Not Designated as Hedging Instrument | Long-term liabilities: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (16,373) (1,284)
Derivative liability, fair value, gross asset 5,237 0
Derivative liability $ (11,136) $ (1,284)