2020 Asset Transactions (Details)		3 Months Ended		9 Months Ended
	May 11, 2020 USD ($) numberOfWells mi	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($) a	Sep. 30, 2020 USD ($) a	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Nonmonetary Transaction
Loss from asset exchange transaction		$ 4,662,000	$ 13,935,000	$ 102,721,000	$ 13,935,000
Derivative instruments, at fair value		894,618,000		894,618,000		$ 312,696,000
2020 Divestiture | Pennsylvania
Nonmonetary Transaction
Miles of gathering lines (in miles) | mi	33
2020 Divestiture | West Virginia
Nonmonetary Transaction
Miles of gathering lines (in miles) | mi	154
Disposal Group, Not Discontinued Operations | 2020 Divestiture
Nonmonetary Transaction
Purchase price	$ 125,000,000
Repayment of asset retirement obligation and other liabilities				49,000,000
Potential contingent consideration		20,000,000		20,000,000
Derivative instruments, at fair value	$ 0	5,100,000		5,100,000
Loss on sale, exchange of long-lived assets				$ 36,800,000
Disposal Group, Not Discontinued Operations | 2020 Divestiture | Pennsylvania
Nonmonetary Transaction
Number of wells sold | numberOfWells	80
Disposal Group, Not Discontinued Operations | 2020 Divestiture | West Virginia
Nonmonetary Transaction
Number of wells sold | numberOfWells	809
Asset Exchange Transaction
Nonmonetary Transaction
Area of acres exchanged (in acres) | a				14,600
Area of acres obtained in asset exchange (in acres) | a				14,600
2019 Asset Exchange Transaction [Member]
Nonmonetary Transaction
Area of acres exchanged (in acres) | a			16,000
Area of acres obtained in asset exchange (in acres) | a			16,000
Additional areas of acres disposed of as consideration (in acres) | a			3,000
Loss from asset exchange transaction		13,900,000
Reimbursement liability recognized		28,700,000		$ 28,700,000		$ 36,800,000
2020 Asset Exchange Transaction [Member]
Nonmonetary Transaction
Loss from asset exchange transaction		$ 11,600,000		$ 67,200,000