Derivative Instruments - Fair Value of Derivative Instruments on a Gross basis and on a Net Basis as Presented in Consolidated Balance Sheets (Detail) - Commodity Contract [Member] - Not Designated as Hedging Instrument [Member] - USD ($) $ in Thousands		Jun. 30, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross Amount		$ 8,832	$ 50
Netting Adjustments	[1]	(6,225)	(50)
Net Amount Presented in Balance Sheets		2,607
Gross Amount		(11,083)	(48,132)
Netting Adjustments	[1]	6,225	50
Net Amount Presented in Balance Sheets		(4,858)	(48,082)
Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		4,549	50
Netting Adjustments	[1]	(4,110)	(50)
Net Amount Presented in Balance Sheets		439
Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		4,283
Netting Adjustments	[1]	(2,115)
Net Amount Presented in Balance Sheets		2,168
Current Liabilities [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		(7,349)	(35,459)
Netting Adjustments	[1]	4,110	50
Net Amount Presented in Balance Sheets		(3,239)	(35,409)
Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		(3,734)	(12,673)
Netting Adjustments	[1]	2,115
Net Amount Presented in Balance Sheets		$ (1,619)	$ (12,673)

[1] The Company has agreements in place that allow for the financial right to offset for derivative assets and derivative liabilities at settlement or in the event of a default under the agreements.