Natural Gas And Oil Producing Activities (Unaudited) (Changes in Proved Natural Gas and Oil Reserves) (Details)	12 Months Ended
	Dec. 31, 2013 MMcf	Dec. 31, 2012 MMcf	Dec. 31, 2011 MMcf
Natural Gas [Member]
Proved reserves, beginning of year	4,016,798	5,887,207	4,929,980
Revisions of previous estimates	325,374	(2,087,985)	34,505
Extensions, discoveries and other additions	3,283,495	918,594	1,459,428
Production	(655,704)	(564,484)	(499,433)
Acquisition of reserves in place	4,114		13
Disposition of reserves in place		(136,534)	(37,286)
Proved reserves, end of year	6,974,077	4,016,798	5,887,207
Proved Developed Reserves [Abstract]
Beginning of year	3,195,662	3,254,018	2,687,238
End of year	4,237,495	3,195,662	3,254,018
Proved Undeveloped Reserves [Abstract]
Beginning of year	821,136	2,633,189	2,242,742
End of year	2,736,582	821,136	2,633,189
Oil [Member]
Proved reserves, beginning of year	244	996	1,219
Revisions of previous estimates	88	(44)	(125)
Extensions, discoveries and other additions	229	154	2
Production	(188)	(83)	(97)
Disposition of reserves in place		(779)	(3)
Proved reserves, end of year	373	244	996
Proved Developed Reserves [Abstract]
Beginning of year	243	983	1,173
End of year	372	243	983
Proved Undeveloped Reserves [Abstract]
Beginning of year	1	13	46
End of year	1	1	13