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		Mar. 31, 2017	Dec. 31, 2016
Derivatives, Fair Value [Line Items]
Gross Amount		$ 7,482	$ 50
Netting Adjustments	[1]	(3,529)	(50)
Net Amount Presented in Balance Sheets		3,953
Gross Amount		(30,231)	(48,132)
Netting Adjustments	[1]	3,529	50
Net Amount Presented in Balance Sheets		(26,702)	(48,082)
Other Current Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		2,118	50
Netting Adjustments	[1]	(2,118)	(50)
Other Noncurrent Assets [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		5,364
Netting Adjustments	[1]	(1,411)
Net Amount Presented in Balance Sheets		3,953
Current Liabilities [Member] | Accrued Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		(26,199)	(35,459)
Netting Adjustments	[1]	2,118	50
Net Amount Presented in Balance Sheets		(24,081)	(35,409)
Noncurrent Liabilities [Member]
Derivatives, Fair Value [Line Items]
Gross Amount		(4,032)	(12,673)
Netting Adjustments	[1]	1,411
Net Amount Presented in Balance Sheets		$ (2,621)	$ (12,673)

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