Oil And Natural Gas Properties (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2011
Effects of cash flow hedges	$ 13.7
Jan'12 - Dec'12 [Member]
Oil and gas production volume covered by hedges that affect ceiling determination (in MMBoe)	4.7
Jan'13 - Dec'13 [Member]
Oil and gas production volume covered by hedges that affect ceiling determination (in MMBoe)	0.7
Oct'11 - Dec'11 [Member]
Oil and gas production volume covered by hedges that affect ceiling determination (in MMBoe)	1.8