Income Taxes (Schedule Of Deferred Tax Assets And Deferred Tax Liabilities) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
Income Tax Disclosure [Abstract]
Net operating loss carryforward	$ 328,874,000	[1],[2]	$ 509,485,000	[1],[2]
Asset retirement obligations	73,623,000		72,391,000
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	67,990,000		51,056,000
Other	74,184,000		107,836,000
Total deferred tax assets	544,671,000		740,768,000
Oil and gas properties, principally due to differences in basis, depletion and the deduction of intangible drilling costs for tax purposes	(1,569,886,000)		(2,322,571,000)
Other property and equipment, principally due to the deduction of bonus depreciation for tax purposes	(254,632,000)		(263,939,000)
State taxes and other	(103,255,000)		(208,058,000)
Net deferred hedge gains	(108,784,000)		(173,097,000)
Total deferred tax liabilities	(2,036,557,000)		(2,967,665,000)
Net deferred tax liability	(1,491,886,000)		(2,226,897,000)
Current deferred income tax liability	(19,169,000)		(86,481,000)
Non-current deferred income tax liability	(1,472,717,000)		(2,140,416,000)
UNITED STATES
Income Tax Disclosure [Abstract]
Net operating loss carryforward	917,400,000
COLORADO
Income Tax Disclosure [Abstract]
Net operating loss carryforward	122,000,000
KANSAS
Income Tax Disclosure [Abstract]
Net operating loss carryforward	50,600,000
Valuation allowances	(1,500,000)
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	$ 32,000,000

[1] Net operating loss carryforwards as of December 31, 2013 consist of $917.4 million of U.S. federal NOLs which expire primarily in 2032, $122.0 million of Colorado NOLs which expire between 2027 and 2033 and $50.6 million of Kansas NOLs which expire between 2018 and 2023.

[2] Net operating loss carryforwards as of December 31, 2013 are net of a $1.5 million valuation allowance relating to $32 million of Kansas NOLs that the Company believes will more likely than not expire unutilized.