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

12 Months Ended

Dec. 31, 2013

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,
	2013			2012			2011
Acquisition costs:
Proved (1)	$	177,880		$	352		$	2,720
Unproved (1)	35,008			15,677			43,207
Divestitures—unproved (2)	(487		)	(8,889		)	(14,461		)
Exploration costs:
Proved	34,344			72,361			92,466
Unproved	20,112			18,033			5,919
Development costs	41,328			18,740			34,400
Capitalized general and administrative and interest costs	19,911			18,961			18,210
Total costs incurred	$	328,096		$	135,235		$	182,461

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

	For the Year-Ended December 31,
	2013			2012			2011
Accumulated depreciation, depletion and amortization (DD&A)
Balance, beginning of year	$	(1,472,244	)	$	(1,265,603	)	$	(1,175,553	)
Provision for DD&A	(69,357		)	(59,496		)	(57,143		)
Ceiling test writedown	—			(137,100		)	(18,907		)
Sale of proved properties and other (3)	(11,443		)	(10,045		)	(14,000		)
Balance, end of year	$	(1,553,044	)	$	(1,472,244	)	$	(1,265,603	)
DD&A per Mcfe	$	1.82		$	1.75		$	1.89