Acquisitions and Dispositions - Dispositions - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets	$ 102,000	$ (2,597,000)			$ 23,509,000	$ (7,544,000)
Western Oklahoma Properties
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets		(2,600,000)		$ (2,700,000)	22,100,000
Proceeds from sale of oil and gas properties		900,000		77,700,000	$ 26,000,000
Miscellaneous Proved, Unproved Properties and Surface Acreage
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets	102,000	30,000	$ 1,300,000	(198,000)
Proceeds from sale of oil and gas properties	$ 295,000	$ 131,000	$ 1,300,000	1,700,000
Northeast Pennsylvania Non-operated Interest
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets						(2,100,000)
Proceeds from sale of oil and gas properties						$ 111,500,000
Mississippi and South Texas properties
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Proceeds from sale of oil and gas properties				$ 1,200,000