Properties and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Components of net property and equipment

Properties and equipment, net are comprised of the following:

	December 31,
(In thousands)	2017			2016
Proved oil and gas properties	$	4,932,512		$	7,437,604
Unproved oil and gas properties	190,474			260,543
Gathering and pipeline systems	1,569			187,846
Land, building and other equipment	82,670			84,462
	5,207,225			7,970,455
Accumulated depreciation, depletion and amortization	(2,135,021		)	(3,720,330		)
	$	3,072,204		$	4,250,125

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)	2017		2016		2015
Balance at beginning of period	$	—	$	—	$	10,557
Additions to capitalized exploratory well costs pending the determination of proved reserves	19,511		—		—
Reclassifications to wells, facilities, and equipment based on the determination of proved reserves	—		—		(10,557		)
Capitalized exploratory well costs charged to expense	—		—		—
Balance at end of period	$	19,511	$	—	$	—

Summary of assets held-for-sale

Balance sheet data related to the assets held for sale is as follows:

(In thousands)	December 31, 2017
ASSETS
Inventories	$	1,440
Properties and equipment, net	778,855
	780,295
LIABILITIES
Accounts payable	2,352
Asset retirement obligations	15,748
	18,100
Net assets held for sale	$	762,195

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)	2017		2016		2015
Capitalized exploratory well costs that have been capitalized for a period of one year or less	$	19,511	$	—	$	—
Capitalized exploratory well costs that have been capitalized for a period greater than one year	—		—		—
	$	19,511	$	—	$	—