Disclosure About Oil and Gas Producing Activities (Unaudited) (Details 6) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Developed Properties [Abstract]
Acquisition, equipment, exploration, drilling and evnironmental costs	$ 5,974,604	$ 4,575,222
Less: Accumulated depletion, depreciation and amortization	(2,322,982)	(1,985,799)
Proved	3,651,622	2,589,423
Unproven Properties:
Oil Gas Properties Using Full Cost Method Accounting Unproved	537,526	486,247
Net capitalized costs - oil and gas properties	$ 4,189,148	$ 3,075,670