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)

v3.8.0.1
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, 2018
Dec. 31, 2017
Offsetting Assets and Liabilities [Line Items]    
Derivative asset $ 4,210 $ 406
Derivative liability 28,854 29,028
Current assets: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative asset, fair value, gross asset 10,638 406
Derivative asset, fair value, gross liability (6,428) 0
Derivative asset 4,210 406
Current liabilities: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (32,340) (27,744)
Derivative liability, fair value, gross asset 6,428 0
Derivative liability 25,912 27,744
Long-term liabilities: Fair value of derivatives    
Offsetting Assets and Liabilities [Line Items]    
Derivative liability, fair value, gross liability (2,942) (1,284)
Derivative liability, fair value, gross asset 0 0
Derivative liability $ 2,942 $ 1,284