Divestiture (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 MMcf	Dec. 31, 2010 MMcf	May 25, 2011 MMcf
Divestiture Abstract
Proceeds from sale of oil and gas property and equipment	$ 118.1	$ 357.8
Divested assets, Haynesville and Middle Bossier Shales, Net acres		20,063	9,717
Net production per day of acreage sold in MMcf		13.5	7.0
Net proved reserves sold in Bcf	37.1	55.4
Restricted cash			85.0
Sales proceeds utilized for like-kind exchange transactions	$ 82.1