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DERIVATIVES AND RISK MANAGEMENT ACTIVITIES Table 2 - Derivative Instruments Eligble for Offset (Details) - Commodity contracts - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Offsetting Assets [Line Items]    
Net amounts of assets presented in the consolidated balance sheets $ 0 $ 155
Net amounts of liabilities presented in the consolidated balance sheets $ (878) $ (5,052)