Disclosure About Oil and Gas Producing Activities (Unaudited) (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Discounted Future Net Cash Flows Relating To Proved Oil And Gas Reserves Future Net Cash Flows Abstract
Future Cash Inflows	$ 9,380,970	$ 22,196,913	$ 19,186,072
Future Production Costs	(3,217,771)	(6,113,282)	(5,253,509)
Future Development Costs	(1,661,394)	(4,294,375)	(3,052,843)
Future Income Taxes	(733,855)	(3,340,516)	(3,198,413)
Future Net Cash Flows	3,767,950	8,448,740	7,681,307
Discount at 10%	(1,873,633)	(4,652,684)	(4,155,739)
Standardized measure of discounted future net cash flows	$ 1,894,317	$ 3,796,056	$ 3,525,568