Natural Gas And Oil Producing Activities (Unaudited) (Analysis of Changes in the Standardized Measure) (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]
Standardized measure, beginning of year	$ 2,050,665	$ 3,450,800	$ 3,013,750
Sales and transfers of natural gas and oil produced, net of production costs	(1,774,043)	(1,443,606)	(1,632,156)
Net changes in prices and production costs	1,852,772	(2,604,591)	(381,131)
Extensions, discoveries, and other additions, net of future production and development costs	1,454,634	549,601	1,163,992
Acquisition of reserves in place	4,914		30
Sales of reserves in place		(157,108)	(11,761)
Revisions of previous quantity estimates	348,996	(1,109,409)	34,221
Accretion of Discount	232,385	480,315	426,245
Net change in income taxes	(1,119,798)	1,079,158	(103,643)
Changes in estimated future development costs	(196,394)	2,475,470	70,492
Previously estimated development costs incurred during the year	222,982	61,949	564,894
Changes in production rates (timing) and other	658,931	(731,914)	305,867
Standardized measure, end of year	$ 3,736,044	$ 2,050,665	$ 3,450,800