Derivative Financial Instruments and Fair Value Measurements - Derivative Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Commodities contracts - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Asset — Commodities contracts	$ 935	$ 11
Liability — Commodities contracts	666	4,328
Level 1
Derivatives, Fair Value [Line Items]
Asset — Commodities contracts	0	0
Liability — Commodities contracts	0	0
Level 2
Derivatives, Fair Value [Line Items]
Asset — Commodities contracts	935	11
Liability — Commodities contracts	666	4,328
Level 3
Derivatives, Fair Value [Line Items]
Asset — Commodities contracts	0	0
Liability — Commodities contracts	$ 0	$ 0