Disclosure About Oil and Gas Producing Activities (Unaudited) (Details 5) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Results of Operations, Oil and Gas Producing Activities Net Income (Excluding Corporate Overhead and Interest Costs) [Abstract]
Oil and gas revenue	$ 1,230,020	$ 933,404	$ 809,974
Production expenses	(280,631)	(212,578)	(184,229)
Depletion and depreciation expense	(292,951)	(243,390)	(388,985)
Write-downs of proved oil and gas properties	0	0	(2,972,464)
Income taxes	3,736	(2,821)	662,698
Total	$ 660,174	$ 474,615	$ (2,073,006)