Divestiture (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2012 MMcf	May 31, 2011 MMcf acre	Dec. 31, 2011
Divestiture [Abstract]
Proceeds from sale of oil and gas property and equipment	$ 168.0	$ 118.1
Divested assets, Production in MMcfe per day	24.0
Divested assets, Proved net reserves in Bcfe			143.0
Divested assets, Haynesville and Middle Bossier Shales, Net acres		9,717
Net production per day of acreage sold in MMcf		7.0
Divested assets, net proved reserves in Bcf		37.1