Oil and Gas Properties, Buildings and Equipment (Details) (USD $)	12 Months Ended											12 Months Ended							12 Months Ended			3 Months Ended
	Dec. 31, 2011		Dec. 31, 2010 Wells		Dec. 31, 2009	Dec. 31, 2011 Machinery, drilling rigs, and equipment	Dec. 31, 2010 Machinery, drilling rigs, and equipment	Dec. 31, 2011 Building and improvements	Dec. 31, 2010 Building and improvements	Dec. 31, 2011 Vehicles	Dec. 31, 2010 Vehicles	Dec. 31, 2009 Denver Julesburg	Dec. 31, 2011 Assets measured on nonrecurring basis Other Long-Lived Assets	Dec. 31, 2010 Assets measured on nonrecurring basis Other Long-Lived Assets	Dec. 31, 2009 Assets measured on nonrecurring basis Other Long-Lived Assets	Dec. 31, 2011 East Texas Assets measured on nonrecurring basis Oil and Gas Properties	Dec. 31, 2011 3 Drilling Rigs Drilling_rigs	Dec. 31, 2009 1 Drilling Rig	Dec. 31, 2011 Unevaluated properties	Dec. 31, 2010 Unevaluated properties	Dec. 31, 2009 Unevaluated properties	Dec. 31, 2011 NYMEX HH
Oil and natural gas:
Proved properties	$ 3,257,321,000	[1]	$ 3,182,305,000	[1]
Unproved properties	228,486,000	[2]	217,253,000	[2]															14,800,000
Oil and natural gas: Proved properties and Unproved properties, gross	3,485,807,000		3,399,558,000
Less accumulated depreciation, depletion and amortization	(962,154,000)		(757,264,000)
Oil and natural gas: Proved and Unproved properties, Net	2,523,653,000		2,642,294,000
Oil and natural gas properties (successful efforts basis), buildings and equipment, net	2,531,393,000		2,655,792,000
Capitalized interest costs as component of property costs for development projects (in months)	6 months
Number of wells encountering mechanical failure			1
Impairment charge related to the write-down of a rig to its fair market value					4,200,000								4,300,000	0	4,200,000
Drilling rigs																	3
Carrying amount before impairment of equipment																	5,700,000	7,500,000
Property, Plant and Equipment, Fair Value Disclosure																	1,400,000	3,300,000
Future strip, average of the daily settlement prices of futures contracts (in years)																						5 years
Future strip, average of the daily settlement prices of futures contracts (in months)																						60 months
Future strip, average of the daily settlement prices of futures contracts, percentage decrease																						15.00%
E. Texas Carrying Amount Prior to Impairment	739,300,000
Impairment of oil and natural gas properties	625,564,000		0		1,017,000											625,000,000			600,000	0	1,017,000
Impairment of Oil and Gas Properties from discontinued operations, before tax												9,600,000
Net earnings from discontinued operations	0		0		6,806,000							6,806,000
Commerical and other:
Commerical and other, gross	37,209,000		39,271,000			22,509,000	24,988,000	6,894,000	7,434,000	7,806,000	6,849,000
Less accumulated depreciation	(29,469,000)		(25,773,000)
Commercial and other, net	$ 7,740,000		$ 13,498,000

[1] Includes cogeneration facilities.

[2] Unproved properties includes acquisition costs for properties to which proved developed producing and proved undeveloped reserves are also attributed. At December 31, 2011, unproved properties included $14.8 million of acquisition costs for unevaluated properties. The Company assesses these properties annually and recorded impairments of $0.6 million, $0.0 million and $1.0 million for the years ended December 31, 2011, 2010 and 2009, respectively.