Supplemental Gas Data Capitalized Costs (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Capitalized Costs Relating to Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proven properties	$ 1,670,404	$ 1,596,838
Unproven properties	1,463,406	1,266,017
Drilling Cost	1,937,336	1,550,297
Wells and related equipment	688,548	492,364
Gathering assets	1,058,008	1,006,882
Oil and Gas Reclamation Liability, Noncurrent	113,481	70,753
Total Property, Plant and Equipment	6,931,183	5,983,151
Accumulated Depreciation, Depletion and Amortization	(1,187,409)	(959,291)
Net Capitalized Costs	$ 5,743,774	$ 5,023,860