Oil And Natural Gas Properties And Equipment (Schedule Of Capitalized Exploratory Well Costs) (Detail)	Dec. 31, 2015 item	Dec. 31, 2014 USD ($) item	Dec. 31, 2013 USD ($) item
Supplemental Information On Oil And Gas Producing Activities [Abstract]
Exploratory well costs capitalized for greater than one year		$ 8,900,000	$ 16,700,000
Total capitalized exploratory well costs		$ 8,900,000	$ 16,700,000
Number of projects capitalized for greater than a year | item	0	1	2