Properties and Equipment (Tables)

12 Months Ended

Dec. 31, 2014

Property, Plant and Equipment [Abstract]

Components of net properties and equipment

Properties and equipment are comprised of the following:

	December 31,
(In thousands)	2014			2013
Proved oil and gas properties	$	7,984,979		$	6,362,570
Unproved oil and gas properties	492,208			375,428
Gathering and pipeline systems	241,272			239,958
Land, building and other equipment	109,758			94,243
	8,828,217			7,072,199
Accumulated depreciation, depletion and amortization	(3,902,506		)	(2,525,972		)
	$	4,925,711		$	4,546,227

Schedule of net changes in capitalized exploratory well costs

The following table reflects the net changes in capitalized exploratory well costs:

	Year Ended December 31,
(In thousands)	2014		2013			2012
Balance at beginning of period	$	—	$	10,390		$	5,328
Additions to capitalized exploratory well costs pending the determination of proved reserves	10,557		—			10,390
Reclassifications to wells, facilities, and equipment based on the determination of proved reserves	—		(10,198		)	—
Capitalized exploratory well costs charged to expense	—		(192		)	(5,328		)
Balance at end of period	$	10,557	$	—		$	10,390

Schedule of aging of capitalized exploratory well costs

The following table provides an aging of capitalized exploratory well costs based on the date the drilling was completed:

	December 31,
(In thousands)	2014		2013		2012
Capitalized exploratory well costs that have been capitalized for a period of one year or less	$	10,557	$	—	$	10,390
Capitalized exploratory well costs that have been capitalized for a period greater than one year	—		—		—
	$	10,557	$	—	$	10,390