Supplemental Gas Data Capitalized Costs (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved Oil and Gas Property, Successful Effort Method	$ 2,016,916	$ 1,922,602
Unproved Oil and Gas Property, Successful Effort Method	1,116,282	1,421,083
Drilling Cost	3,583,565	3,452,989
Wells and related equipment	791,996	785,744
Gathering assets	1,138,299	1,147,173
Oil and Gas Reclamation Liability, Noncurrent	176,961	115,121
Total Property, Plant and Equipment	8,824,019	8,844,712
Accumulated Depreciation, Depletion and Amortization	(3,099,622)	(2,691,005)
Net Capitalized Costs	5,724,397	6,153,707
Gas Segment [Member]
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved Oil and Gas Property, Successful Effort Method		1,922,602
Unproved Oil and Gas Property, Successful Effort Method		1,421,083
Drilling Cost	$ 3,583,565	$ 3,452,989