Results of Operations for Oil and Gas Producing Activities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2009
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Other operating revenues, anticipated recovery of federal royalties paid	$ 244.4	[1]

[1] Results exclude corporate overhead, interest and discontinued operations.