Suspended Exploratory Well Costs - Suspended Exploratory Well Costs (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) Project	Dec. 31, 2015 USD ($) Project	Dec. 31, 2014 USD ($) Project
Extractive Industries [Abstract]
Balance at beginning of period	$ 4,161	$ 2,996	$ 6,964
Additions to capitalized exploratory well costs pending the determination of proved reserves	9,128	1,165	18,747
Reclassifications to wells, facilities and equipment based on determination of proved reserves	(5,877)	0	(15,735)
Capitalized exploratory well costs charged to expense	0	0	(6,980)
Balance at end of period	7,412	4,161	2,996
Less exploratory well costs that have been capitalized for a period of one year or less	(7,412)	(1,165)	(2,996)
Capitalized exploratory well costs that have been capitalized for a period greater than one year	$ 0	$ 2,996	$ 0
Number of projects that have exploratory well costs that have been capitalized for a period greater than one year | Project	0	1	0