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Fair Value Measurements Fair Value Measurements - Recurring (Details)
Jun. 30, 2017
Embedded derivatives in commodity contracts | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]  
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]  
Derivative Liability, Number of Instruments Held 2