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Long-Term Debt (Details Textuals)			1 Months Ended			2 Months Ended	3 Months Ended				9 Months Ended	12 Months Ended
Long-Term Debt (Details Textuals)	Oct. 31, 2020 USD ($)	Sep. 18, 2020 USD ($)	Mar. 31, 2020 USD ($)	Jul. 31, 2019 USD ($)	Jun. 30, 2019 USD ($)	May 31, 2018 shares	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Sep. 18, 2020 USD ($) shares	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares	Aug. 07, 2020 USD ($)	Sep. 30, 2019 USD ($)
Debt Instrument [Line Items]
Interest in guarantor subsidiaries							100.00%					100.00%
Principal amount of debt cancelled		$ 2,100,000,000
Lease period included in long-term transportation service agreement												20 years
Letters of credit outstanding under DIP Facility															$ 41,300,000
Shares issued upon conversion of notes \| shares						55,200,000			7,400,000
Debt principal balance net of debt discounts reclassified to equity									$ 13,900,000
Cash paid for debt repurchases			$ 14,200,000				$ 0				$ 14,171,000		$ 0	$ 0
Gain on debt extinguishment			19,000,000.0				0				18,994,000		155,998,000	$ 0
Cash paid for debt repurchases or exchanges					$ 120,000,000.0			$ 5,300,000		$ 11,200,000
Debt discount							0			101,767,000		$ 0	101,767,000
Unamortized debt issuance costs							8,400,000			$ 14,000,000.0		8,400,000	$ 14,000,000.0
Senior Secured Bank Credit Facility [Abstract]
Borrowing base							575,000,000					575,000,000
Lender commitments		$ 575,000,000					$ 575,000,000				$ 575,000,000	$ 575,000,000
Percentage reduction of borrowing base upon issuing or incurring unsecured debt, expressed as a percentage of the principal amount of unsecured debt							25.00%					25.00%
Floor interest rate							1.00%
Weighted average interest rate							4.00%
Commitment fee percentage							0.50%
Common Stock
Debt Instrument [Line Items]
Shares issued upon conversion of notes \| shares											7,372,250			55,249,955
Issuance of new shares, shares \| shares										38,300,000	49,999,999		36,297,217
Free State Pipeline
Debt Instrument [Line Items]
Payments to reacquire pipeline	$ 22,500,000
NEJD Pipeline
Debt Instrument [Line Items]
Payments to reacquire pipeline	$ 70,000,000
Letter of Credit
Senior Secured Bank Credit Facility [Abstract]
Line of credit facility, capacity available for specific purpose other than for trade purchases							$ 100,000,000					$ 100,000,000
Swingline Loan
Senior Secured Bank Credit Facility [Abstract]
Line of credit facility, capacity available for specific purpose other than for trade purchases							$ 25,000,000					$ 25,000,000
Minimum
Senior Secured Bank Credit Facility [Abstract]
Percentage threshold for borrowing base property sales or hedge terminations that would prompt a borrowing base reduction.							5.00%					5.00%
Current ratio requirement							1.0
Minimum \| Dividend or Other Restricted Payment
Senior Secured Bank Credit Facility [Abstract]
Borrowing base availability requirement							20.00%					20.00%
Maximum
Senior Secured Bank Credit Facility [Abstract]
Consolidated total debt to consolidated EBITDAX requirement							3.5
Maximum \| Dividend or Other Restricted Payment
Senior Secured Bank Credit Facility [Abstract]
Consolidated total debt to consolidated EBITDAX requirement							2
London Interbank Offered Rate (LIBOR) \| Minimum
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on senior secured bank credit facility							3.00%
London Interbank Offered Rate (LIBOR) \| Maximum
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on senior secured bank credit facility							4.00%
Base Rate \| Minimum
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on senior secured bank credit facility							2.00%
Base Rate \| Maximum
Senior Secured Bank Credit Facility [Abstract]
Interest rate margins on senior secured bank credit facility							3.00%
9% Senior Secured Second Lien Notes due 2021
Debt Instrument [Line Items]
Debt repurchases, face amount			$ 30,200,000
7 3/4% Senior Secured Second Lien Notes due 2024
Debt Instrument [Line Items]
Debt discount					22,600,000
6 3/8% Convertible Senior Notes due 2024
Debt Instrument [Line Items]
Debt principal of notes converted									$ 19,900,000
Face value of notes					245,500,000
Debt discount					79,900,000
6 3/8% Senior Subordinated Notes due 2021
Debt Instrument [Line Items]
Amount of debt exchanged					152,200,000
5 1/2% Senior Subordinated Notes due 2022
Debt Instrument [Line Items]
Debt repurchases, face amount										$ 25,300,000			$ 25,300,000			$ 11,000,000.0
Amount of debt exchanged					219,900,000
4 5/8% Senior Subordinated Notes due 2023
Debt Instrument [Line Items]
Debt repurchases, face amount										$ 75,700,000			75,700,000
Amount of debt exchanged					96,300,000
Senior Subordinated Notes
Debt Instrument [Line Items]
Amount of debt exchanged					468,400,000
Notes Repurchases
Debt Instrument [Line Items]
Gain on debt extinguishment													55,500,000
Portion Of Exchange Related To Senior Secured Notes
Debt Instrument [Line Items]
Gain on debt extinguishment					0
Portion Of Exchange Related To Senior Secured Notes \| 7 3/4% Senior Secured Second Lien Notes due 2024
Debt Instrument [Line Items]
Face value of notes				$ 3,800,000	425,400,000
Unamortized debt issuance costs					6,900,000
Portion Of Exchange Related To Senior Secured Notes \| 7 1/2% Senior Secured Second Lien Notes due 2024
Debt Instrument [Line Items]
Amount of debt exchanged				$ 4,000,000.0	425,400,000
Notes Exchange
Debt Instrument [Line Items]
Gain on debt extinguishment													$ 100,500,000
Notes Exchange \| 7 3/4% Senior Secured Second Lien Notes due 2024
Debt Instrument [Line Items]
Face value of notes					$ 102,600,000