Suspended Exploratory Well Costs - Suspended Exploratory Well Costs (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) Project
Extractive Industries [Abstract]
Balance at beginning of period	$ 4,161	$ 2,996
Additions to capitalized exploratory well costs pending the determination of proved reserves	1,214	1,165
Reclassifications to wells, facilities and equipment based on determination of proved reserves	(5,375)
Balance at end of period		4,161
Less exploratory well costs that have been capitalized for a period of one year or less		(1,165)
Capitalized exploratory well costs that have been capitalized for a period greater than one year	$ 0	$ 2,996
Number of projects that have exploratory well costs that have been capitalized greater than one year | Project		1