Derivative Instruments and Hedging Activities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($) payment	Jun. 30, 2017 USD ($) $ / bbl	Dec. 31, 2016 USD ($)
Derivative [Line Items]
Number of contingent payments | payment	2
FCX Settlement
Derivative [Line Items]
Derivative contingent settlement period		12 months
FCX Settlement | Noble Corp
Derivative [Line Items]
Estimated fair value of contingent payments		$ 0
FCX Settlement | WTI Crude Oil Averages Price More than $50 Per Barrel
Derivative [Line Items]
Crude oil average price | $ / bbl		50
Non designated derivatives contingent payment		$ 25,000,000
FCX Settlement | WTI Crude Oil Averages Price More than $65 Per Barrel
Derivative [Line Items]
Crude oil average price | $ / bbl		65
Non designated derivatives contingent payment		$ 50,000,000
Forward contracts
Derivative [Line Items]
Derivative Instrument Settlement Amount	$ 37,600,000		$ 53,100,000
Price risk derivative
Derivative [Line Items]
Notional amount of forward contracts outstanding	$ 0		$ 0