Property, Plant And Equipment (Aging of Capitalized Exploratory Well Costs) (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2014 item	Sep. 30, 2013 item	Dec. 31, 2013	Dec. 31, 2012
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount	$ 406,625	$ 421,000	$ 393,030	$ 445,697
No. of Wells	32	38
No. of Projects	9	10
Zero to one year [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount	32,192	36,424
No. of Wells	2	2
No. of Projects	1	2
One to two years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount	36,676	51,444
No. of Wells	2	6
No. of Projects	1
Two to three years [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount	51,898	35,504
No. of Wells	6	3
No. of Projects		3
Three years or more [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Amount	$ 285,859	$ 297,628
No. of Wells	22	27
No. of Projects	7	5