Oil and Gas Producing Activities (Tables)

12 Months Ended

Dec. 31, 2017

Oil And Gas Exploration And Production Industries Disclosures [Abstract]

Capitalized Costs Related to Oil and Gas Property Acquisition Exploration and Development Activities

Capitalized Costs

	As of December 31,
	2016			2017
	(In thousands)
Proved properties:
Leasehold costs	$	662,022		$	491,507
Wells and related equipment and facilities		3,135,079			2,140,243
Accumulated depreciation depletion and amortization		(3,009,236	)		(2,032,927	)
	$	787,865		$	598,823

Costs Incurred Related to Oil and Gas Property Acquisition Exploration and Development Activities

Costs Incurred

	For the Years Ended December 31,
	2015		2016		2017
	(In thousands)
Unproved property acquisitions	$	12,972	$	—	$	—
Development costs		221,265		58,587		177,432
Exploration costs		12,265		—		—
	$	246,502	$	58,587	$	177,432