Income Taxes (Components of Deferred Tax Assets and Liabilities) (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred tax assets
Loss carryforwards - federal	$ 20,247	$ 0
Loss carryforwards - state	41,379	35,007
Tax credit carryover	34,837	34,837
Derivative contracts	21,341	7,252
Enhanced oil recovery credit carryforwards	14,974	17,346
Stock-based compensation	34,635	28,387
Other	37,679	37,226
Total deferred tax assets	205,092	160,055
Deferred tax liabilities
Property and equipment	(2,541,426)	(2,277,388)
Other	(10,206)	(6,963)
Total deferred tax liabilities	(2,551,632)	(2,284,351)
Total net deferred tax liability	$ (2,346,540)	$ (2,124,296)