Disclosures About Fair Value Measurements (Measured On A Nonrecurring Basis) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of oil and gas properties	$ 1,495,242,000	$ 0	$ 354,408,000
Management oil price outlook	80.40	87.09	92.69
Management gas price outlook	4.43	4.78	5.14
South Texas Edwards And Austin Chalk [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Asset Group			189,900,000
Impairment of oil and gas properties			354,400,000
Barnett Shale Field [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Asset Group		184,800,000
Impairment of oil and gas properties		532,600,000
Raton Field [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value of Asset Group	533,600,000
Impairment of oil and gas properties	$ 1,495,200,000