Oil And Natural Gas Properties (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011
Effects of cash flow hedges	$ 37.1
Jul'11 - Dec'11 [Member]
Oil and gas production volume covered by hedges that affect ceiling determination (in MMBoe)	3,300,000
Jan'12 - Dec'12 [Member]
Oil and gas production volume covered by hedges that affect ceiling determination (in MMBoe)	4,400,000
Jan'13 - Dec'13 [Member]
Oil and gas production volume covered by hedges that affect ceiling determination (in MMBoe)	700,000