Derivative Financial Instruments and Fair Value Measurements - Derivatives Recorded at Fair Value in Consolidated Balance Sheets (Details) - Not designated as hedging instruments - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 2,056	$ 1,431
Derivative Liabilities	310	1,844
Current | Commodities contracts
Derivatives, Fair Value [Line Items]
Derivative Assets	2,056	1,431
Derivative Liabilities	310	1,829
Non-current | Commodities contracts
Derivatives, Fair Value [Line Items]
Derivative Assets	0	0
Derivative Liabilities	$ 0	$ 15