Quarterly report pursuant to Section 13 or 15(d)

Organization and Accounting Policies (Assets and Liabilities Measured on Recurring Basis) (Details)

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Organization and Accounting Policies (Assets and Liabilities Measured on Recurring Basis) (Details) - USD ($)
$ in Thousands
Jun. 30, 2019
Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative asset commodity $ 1,956 $ 3,520
Assets 1,956 3,520
SARs liability 1,777 1,007
SARs liability 421 625
Liabilities 2,198 1,632
Level 2 [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Derivative asset commodity 1,956 3,520
Assets 1,956 3,520
SARs liability 1,777 1,007
SARs liability 421 625
Liabilities $ 2,198 $ 1,632