Oil and Gas Properties, Buildings and Equipment (Tables)

12 Months Ended

Dec. 31, 2011

Oil and Gas Properties, Buildings and Equipment [Abstract]

Schedule of Oil and Gas Properties, Building and Equipment Activities

	Year Ended December 31,
(in thousands)	2011			2010
Oil and natural gas:
Proved properties(1)	$	3,257,321		$	3,182,305
Unproved properties(2)	228,486			217,253
	3,485,807			3,399,558
Less accumulated depreciation, depletion and amortization	(962,154		)	(757,264		)
	2,523,653			2,642,294
Commercial and other:
Machinery, drilling rigs, and equipment	22,509			24,988
Buildings and improvements	6,894			7,434
Vehicles	7,806			6,849
	37,209			39,271
Less accumulated depreciation	(29,469		)	(25,773		)
	7,740			13,498
	$	2,531,393		$	2,655,792

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(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.