Fair Value Measurements - Schedule of Fair Value Measured on a Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total fair value	$ (21,085)	$ (5,068)
Commodity Contract [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total fair value	(21,085)	(5,068)
Level 2 [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total fair value	(21,085)	(5,068)
Level 2 [Member] | Commodity Contract [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Total fair value	$ (21,085)	$ (5,068)