Dispositions - Additional Information (Detail)	1 Months Ended	3 Months Ended				6 Months Ended		9 Months Ended
	Aug. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) a	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets		$ (9,230,000)		$ (36,341,000)				$ 112,443,000	$ (30,663,000)
Proceeds from disposal of assets								246,083,000	$ 784,527,000
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		(1,100,000)		117,000		$ (833,000)	$ (187,000)
Proceeds from sale of oil and gas properties		11,000		161,000		$ 71,000	$ 366,000
North Louisiana
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets	$ (8,100,000)
Fair value of total consideration for sale	260,000,000.0
Proceeds from disposal of assets	245,000,000.0
Divestiture fee obligation	479,800,000
Unrealized loss for novated derivatives								12,100,000
North Louisiana | Contingent Consideration
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Estimated fair value of contingent consideration	15,000,000.0	$ 15,000,000.0						15,000,000.0
North Louisiana | Contingent Consideration | Maximum
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Potential contractual payout of contingent consideration	$ 90,000,000.0							$ 90,000,000.0
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
Proceeds from sale of oil and gas properties				$ 750,000,000.0	$ 34,000,000.0
Percentage of royalty disposed				2.50%					2.50%
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
Northwest Pennsylvania
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
(Loss) gain on the sale of assets			$ 122,500,000
Proceeds from sale of oil and gas properties			$ 1,000,000.0