Suspended Exploratory Well Costs - Suspended Exploratory Well Costs (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($) Project	Dec. 31, 2014 USD ($) Project	Dec. 31, 2013 USD ($) Project
Extractive Industries [Abstract]
Balance at beginning of period	$ 2,996	$ 6,964	$ 57,360
Additions to capitalized exploratory well costs pending the determination of proved reserves	1,165	18,747	39,832
Reclassifications to wells, facilities and equipment based on determination of proved reserves	0	(15,735)	(84,840)
Capitalized exploratory well costs charged to expense	0	(6,980)	(5,388)
Balance at end of period	4,161	2,996	6,964
Less exploratory well costs that have been capitalized for a period of one year or less	(1,165)	(2,996)	0
Capitalized exploratory well costs that have been capitalized for a period greater than one year	$ 2,996	$ 0	$ 6,964
Number of projects that have exploratory well costs that have been capitalized for a period greater than one year | Project	1	0	1