Derivative Instruments - Fair Value Amounts of Derivative Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	$ 26,387	$ 109,494
Gross Amounts Offset in the Balance Sheet	(7,161)	(1,039)
Net Amounts of Assets Presented in the Balance Sheet	19,226	108,455
Gross Amounts of Recognized Liabilities	(7,236)	(1,039)
Gross Amounts Offset in the Balance Sheet	7,161	1,039
Net Amounts of Liabilities Presented in the Balance Sheet	(75)	0
Derivative assets (current)
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	18,554	82,205
Gross Amounts Offset in the Balance Sheet	(6,390)	(1,039)
Net Amounts of Assets Presented in the Balance Sheet	12,164	81,166
Derivative assets (noncurrent)
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	7,833	27,289
Gross Amounts Offset in the Balance Sheet	(771)	0
Net Amounts of Assets Presented in the Balance Sheet	7,062	27,289
Accounts payable and accrued liabilities
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities	(6,465)	(1,039)
Gross Amounts Offset in the Balance Sheet	6,390	1,039
Net Amounts of Liabilities Presented in the Balance Sheet	(75)	0
Other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities	(771)	0
Gross Amounts Offset in the Balance Sheet	771	0
Net Amounts of Liabilities Presented in the Balance Sheet	$ 0	$ 0