Investment in Oil and Gas Properties Investment in Oil and Gas Properties (Tables)

12 Months Ended

Dec. 31, 2012

Oil and Gas Exploration and Production Industries Disclosures [Abstract]

Costs Incurred in Oil and Gas Property Acquisition

Costs Incurred in Oil and Gas Property Acquisition, Exploration and Development Activities

(amounts in thousands)

	For the Year-Ended December 31,
	2012			2011			2010
Acquisition costs:
Proved	$	352		$	2,720		$	10,421
Unproved	15,677			43,207			11,310
Divestitures—unproved (1)	(8,889		)	(14,461		)	(36,139		)
Exploration costs:
Proved	72,361			92,466			34,310
Unproved	18,033			5,919			10,384
Development costs	18,740			34,400			34,286
Capitalized general and administrative and interest costs	18,961			18,210			19,665
Total costs incurred	$	135,235		$	182,461		$	84,237

Rollforward of Accumulated Depreciation, Depletion and Amortization of Oil and Gas Producing Activities

	For the Year-Ended December 31,
	2012			2011			2010
Accumulated depreciation, depletion and amortization (DD&A)
Balance, beginning of year	$	(1,265,603	)	$	(1,175,553	)	$	(1,082,381	)
Provision for DD&A	(59,496		)	(57,143		)	(58,172		)
Ceiling test writedown	(137,100		)	(18,907		)	—
Sale of proved properties and other (2)	(10,045		)	(14,000		)	(35,000		)
Balance, end of year	$	(1,472,244	)	$	(1,265,603	)	$	(1,175,553	)
DD&A per Mcfe	$	1.75		$	1.89		$	1.88