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)

v3.19.1
Derivative Instruments and Hedging Activities (Schedule of Derivative Instruments in Statement of Financial Position, Fair Value) (Details) - Not Designated as Hedging Instrument - USD ($)
$ in Thousands
Mar. 31, 2019
Dec. 31, 2018
Offsetting Assets and Liabilities [Line Items]    
Derivative asset $ 11,757 $ 65,114
Derivative liability (31,533) (17,920)
Current assets: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 20,540 78,091
Derivative asset, fair value, gross liability (9,168) (12,977)
Derivative asset 11,372 65,114
Long-term assets: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 829  
Derivative asset, fair value, gross liability (444)  
Derivative asset 385  
Current liabilities: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (33,718) (23,457)
Derivative liability, fair value, gross asset 9,168 12,977
Derivative liability (24,550) (10,480)
Long-term liabilities: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (7,427) (7,440)
Derivative liability, fair value, gross asset 444 0
Derivative liability $ (6,983) $ (7,440)