Properties and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2012

Properties and Equipment, Net

Components of net property, plant, and equipment

	December 31,
(In thousands)	2012			2011
Proved oil and gas properties	$	5,724,940		$	5,006,846
Unproved oil and gas properties		467,483			478,942
Gathering and pipeline systems		239,656			238,660
Land, building and other equipment		86,137			80,908
		6,518,216			5,805,356
Accumulated depreciation, depletion and amortization		(2,207,239	)		(1,870,772	)
	$	4,310,977		$	3,934,584

Schedule of net changes in capitalized exploratory well costs

	Year Ended December 31,
(In thousands)	2012			2011			2010
Beginning balance at January 1	$	5,328		$	4,285		$	4,179
Additions to capitalized exploratory well costs pending the determination of proved reserves		10,390			5,328			4,285
Reclassifications to wells, facilities, and equipment based on the determination of proved reserves		—			(1,138	)		(4,148	)
Capitalized exploratory well costs charged to expense		(5,328	)		(3,147	)		(31	)
Ending balance at December 31	$	10,390		$	5,328		$	4,285

Schedule of aging of capitalized exploratory well costs

	December 31,
(In thousands)	2012		2011		2010
Capitalized exploratory well costs that have been capitalized for a period of one year or less	$	10,390	$	5,328	$	4,285
Capitalized exploratory well costs that have been capitalized for a period greater than one year		—		—		—
	$	10,390	$	5,328	$	4,285