Quarterly report pursuant to Section 13 or 15(d)

Derivatives And Fair Value (Derivative Instruments Accounted For At Fair Value On A Recurring Basis) (Details)

v3.7.0.1
Derivatives And Fair Value (Derivative Instruments Accounted For At Fair Value On A Recurring Basis) (Details) - Commodity Contract [Member] - Not Designated as Hedging Instrument [Member] - Prepayments and other [Member] - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]    
Derivative instruments $ 1,176 $ 1,227
Fair Value, Inputs, Level 1 [Member]    
Derivatives, Fair Value [Line Items]    
Derivative instruments
Fair Value, Inputs, Level 2 [Member]    
Derivatives, Fair Value [Line Items]    
Derivative instruments 1,176 1,227
Fair Value, Inputs, Level 3 [Member]    
Derivatives, Fair Value [Line Items]    
Derivative instruments