Derivative Instruments - Fair Value Amounts of Derivative Instruments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	$ 109,494	$ 656
Gross Amounts Offset in the Balance Sheet	(1,039)	(656)
Net Amounts of Assets Presented in the Balance Sheet	108,455	0
Gross Amounts of Recognized Liabilities	(1,039)	(25,714)
Derivative Liability, Fair Value, Gross Asset	1,039	656
Net Amounts of Liabilities Presented in the Balance Sheet	0	(25,058)
Derivative assets current
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	82,205	594
Gross Amounts Offset in the Balance Sheet	(1,039)	(594)
Net Amounts of Assets Presented in the Balance Sheet	81,166	0
Derivative assets non-current
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Assets	27,289	62
Gross Amounts Offset in the Balance Sheet	0	(62)
Net Amounts of Assets Presented in the Balance Sheet	27,289	0
Derivative liabilities
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities	(1,039)	(21,534)
Derivative Liability, Fair Value, Gross Asset	1,039	594
Net Amounts of Liabilities Presented in the Balance Sheet	0	(20,940)
Derivatives and other noncurrent liabilities
Derivatives, Fair Value [Line Items]
Gross Amounts of Recognized Liabilities	0	(4,180)
Derivative Liability, Fair Value, Gross Asset	0	62
Net Amounts of Liabilities Presented in the Balance Sheet	$ 0	$ (4,118)