Commitments and Contingencies (Narrative) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) case lease	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 8,470,000
Guarantee obligations relative to the firms transportation agreements and gathering project and services	293,000
Contractual commitments assumed by buyer	108,000
Potential amount to be reimbursed to buyer	58,000
Liability for estimated future payments	46,000		$ 88,000
Maturities of operating leases (ASC 842):
2020	41,000
2021	33,000
2022	22,000
2023	19,000
2024	15,000
Thereafter	52,000
Obligation under transportation, 1 to 3 years	1,235,000
Obligation under transportation, 3 to 5 years	1,169,000
Obligation under transportation, 5 to 8 years	1,739,000
Obligation under transportation, more than 8 years	3,559,000
Indemnification liability	$ 0
Appalachian Basin
Commitments And Contingencies [Line Items]
Obligation under transportation agreements		$ 357,000
Maturities of operating leases (ASC 842):
Obligation under transportation agreements, reimbursed by seller		$ 133,000
Arkansas Royalty Litigation
Maturities of operating leases (ASC 842):
Number of cases | case	3
Arkansas Royalty Litigation | Arkansas State Court
Maturities of operating leases (ASC 842):
Number of cases | case	2
Regulatory Approval and or Construction Subsequently Cancelled
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 512,000
Maturities of operating leases (ASC 842):
Other commitment term	17 years
Obligation under transportation, 1 to 3 years	$ 6,000
Obligation under transportation, 3 to 5 years	68,000
Obligation under transportation, 5 to 8 years	102,000
Obligation under transportation, more than 8 years	336,000
Pressure Pumping Equipment | Exploration and Production
Commitments And Contingencies [Line Items]
Aggregate annual lease payment	$ 6,000
Drilling Rigs | Exploration and Production
Commitments And Contingencies [Line Items]
Number of leases | lease	7
Aggregate annual lease payment	$ 13,000
Office Space, Vehicles And Equipment
Maturities of operating leases (ASC 842):
2020	33,000
2021	24,000
2022	18,000
2023	16,000
2024	12,000
Thereafter	45,000
Compression Rentals
Maturities of operating leases (ASC 842):
2020	13,000
2021	13,000
2022	9,000
2023	2,000
Access Capacity on Future Projects Concentration Risk
Commitments And Contingencies [Line Items]
Obligation under transportation agreements	$ 1,100,000