Dispositions - Additional Information (Detail)	3 Months Ended			6 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) a	Sep. 30, 2018 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets	$ (36,341,000)		$ (30,000)			$ (30,663,000)	$ 149,000
Pennsylvania
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets	$ (36,500,000)	$ 5,900,000
Percentage of royalty disposed	2.50%					2.50%
Proceeds from leases	$ 750,000,000.0
Proceeds from sale of oil and gas properties		$ 34,000,000.0
Pennsylvania | Natural Gas and Oil Properties
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of acres sold | a		20,000
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	117,000		9,000	$ (187,000)	$ 179,000
Proceeds from sale of oil and gas properties	$ 161,000		673,000	$ 366,000	$ 366,000
Northern Oklahoma
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets			(39,000)
Proceeds from sale of oil and gas properties			$ 23,300,000