Suspended Exploratory Well Costs - Suspended Exploratory Well Costs (Detail) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Extractive Industries [Abstract]
Balance at beginning of period	$ 2,996	$ 6,964
Additions to capitalized exploratory well costs pending the determination of proved reserves	61,493	18,747
Reclassifications to wells, facilities and equipment based on determination of proved reserves	0	(15,735)
Divested wells	0	(6,980)
Balance at end of period	64,489	2,996
Less exploratory well costs that have been capitalized for a period of one year or less	(64,489)	(2,996)
Capitalized exploratory well costs that have been capitalized for a period greater than one year	$ 0	$ 0