Natural Gas And Oil Producing Activities (Unaudited) (Results of Operations from Natural Gas and Oil Producing Activities) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Natural Gas And Oil Properties [Abstract]
Sales	$ 2,404,165	$ 1,963,172	$ 2,098,914
Production (lifting) costs	(628,817)	(505,271)	(469,153)
Depreciation, depletion and amortization	(735,215)	(765,192)	(666,107)
Impairment of natural gas and oil properties		(1,939,734)
Results of operations - income before income taxes	1,040,133	(1,247,025)	963,654
Provision (benefit) for income taxes	416,042	(496,738)	375,435
Results of operations	$ 624,091	$ (750,287)	$ 588,219