Disclosure About Oil and Gas Producing Activities (Unaudited) (Details 6) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Proven Properties [Abstract]
Acquisition, equipment, exploration, drilling and evnironmental costs	$ 7,235,765	$ 5,974,604
Less: Accumulated depletion, depreciation and amortization	(5,578,265)	(2,322,982)
Proved	1,657,500	3,651,622
Unproven Properties:
Oil Gas Properties Using Full Cost Method Accounting Unproved	0	537,526
Net capitalized costs - oil and gas properties	$ 1,657,500	$ 4,189,148