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Long-Term Debt - Additional Information (Details) |  |  | 3 Months Ended | 12 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2021 | May 01, 2020 USD ($) | Dec. 31, 2020 USD ($) day | Dec. 31, 2020 USD ($) day | Dec. 31, 2019 USD ($) | Dec. 31, 2018 USD ($) | Oct. 08, 2020 USD ($) | Jul. 27, 2020 USD ($) | Mar. 31, 2020 USD ($) | Nov. 25, 2019 USD ($) | Jul. 31, 2019 USD ($)
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Write off of unamortized issuance costs on debt subject to compromise |  |  |  | $ 21,956,000 |  |  |  |  |  |  |
Debtor-in-possession financing, letters of credit outstanding |  |  | $ 262,500,000 | 262,500,000 |  |  |  |  |  |  |
Debtor-in-possession financing, amount arranged |  |  | 105,000,000 | 105,000,000 |  |  |  |  |  |  |
Debtor-in-possession financing, borrowings outstanding |  |  | $ 157,500,000 | 157,500,000 |  |  |  |  |  |  |
DIP credit facility financing fees |  |  |  | $ 2,988,000 |  |  |  |  |  |  |
Debtor-in-possession financing, number of business days after petition date to terminate | day |  |  | 3 | 3 |  |  |  |  |  |  |
Debtor-in-possession financing, number of dates after the entry of the interim order to terminate | day |  |  | 35 | 35 |  |  |  |  |  |  |
Gain on extinguishment of debt |  |  |  | $ 49,579,000 | $ 48,630,000 | $ 0 |  |  |  |  |
Capitalized interest |  |  |  | (907,000) | (3,372,000) | (4,470,000) |  |  |  |  |
Oil and gas properties |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Capitalized interest |  |  |  | (900,000) | (3,400,000) | $ (4,500,000) |  |  |  |  |
Senior notes |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Authorized amount |  |  | $ 200,000,000 | 200,000,000 |  |  |  |  |  |  | $ 100,000,000
Repurchased face amount |  |  | 73,300,000 | 73,300,000 |  |  |  |  |  |  |
Repayments of debt |  |  |  | 22,800,000 |  |  |  |  |  |  |
Gain on extinguishment of debt |  |  |  | 49,600,000 |  |  |  |  |  |  |
Senior notes | Carrying value |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Outstanding debt |  |  | 1,800,000,000 | 1,800,000,000 |  |  |  |  |  |  |
Senior notes | Fair value |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Outstanding debt |  |  | 1,200,000,000 | $ 1,200,000,000 |  |  |  |  |  |  |
Building Loan |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Fixed interest rate on outstanding principal |  |  |  | 4.50% |  |  |  |  |  |  |
Credit facility |  |  | 21,900,000 | $ 21,900,000 |  |  |  |  |  |  |
DIP credit facility | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Weight average interest rate |  |  |  | 5.50% |  |  |  |  |  |  |
DIP credit facility | Revolving credit facility | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment fee percentage |  |  |  | 0.50% |  |  |  |  |  |  |
DIP credit facility | Letter of credit | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Commitment fee percentage |  |  |  | 0.20% |  |  |  |  |  |  |
DIP credit facility | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  | 157,500,000 | $ 157,500,000 | 0 |  |  |  |  |  |
DIP credit facility | Eurodollar | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  | 4.50% |  |  |  |  |  |  |
DIP credit facility | Base Rate | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Interest rate |  |  |  | 3.50% |  |  |  |  |  |  |
Pre-petition revolving credit facility | Revolving credit facility |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Borrowing base |  |  |  |  | 700,000,000 |  | $ 580,000,000 |  |  |  |
Long-term debt |  |  | 292,900,000 | $ 292,900,000 |  |  |  |  |  |  |
Repayments of lines of credit |  |  |  | $ 1,300,000 |  |  |  |  |  |  |
Pre-petition revolving credit facility | Revolving credit facility | Nova Scotia, Amegy, KeyBank |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Proceeds from line of credit |  |  | 96,200,000 |  |  |  |  |  |  |  |
Pre-petition revolving credit facility | Revolving credit facility | Line of Credit | Nova Scotia, Amegy, KeyBank |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Weight average interest rate |  |  |  | 3.15% |  |  |  |  |  |  |
Pre-petition revolving credit facility | Letter of credit |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Maximum repayment amount |  |  |  |  |  |  |  | $ 750,000,000 |  |  |
Pre-petition revolving credit facility | Letter of credit | Nova Scotia, Amegy, KeyBank |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Borrowing base |  | $ 700,000,000.0 |  |  |  |  |  |  | $ 1,000,000,000.0 | $ 1,200,000,000 |
Maximum net secured debt to EBITDAX ratio |  | 2.00 |  |  |  |  |  |  |  |  |
Proceeds from line of credit |  |  | 171,800,000 |  |  |  |  |  |  |  |
Pre-petition revolving credit facility | Letter of credit | Nova Scotia, Amegy, KeyBank | Prepaid Expenses and Other Current Assets |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term line of credit outstanding |  |  | 111,800,000 | $ 111,800,000 |  |  |  |  |  |  |
Pre-petition revolving credit facility | Letter of credit | Nova Scotia, Amegy, KeyBank | Forecast |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Net funded debt to EBITDAX ratio | 4.00 |  |  |  |  |  |  |  |  |  |
Pre-petition revolving credit facility | Letter of credit | Line of Credit | Nova Scotia, Amegy, KeyBank |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term line of credit outstanding |  |  | 147,500,000 | 147,500,000 |  |  |  |  |  |  |
Pre-petition revolving credit facility | Line of Credit |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |
Long-term debt |  |  | $ 292,910,000 | $ 292,910,000 | $ 120,000,000 |  |  |  |  |  |

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- Definition Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=120520924&loc=SL6031897-161870 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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- Definition Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=121572278&loc=d3e13433-108611 + Details
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- Definition Face (par) amount of the original debt instrument that was repurchased. + References No definition available. + Details
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- Definition Amount debtor-in-possession financing arranged (but not necessarily all borrowed). + References No definition available. + Details
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- Definition Amount of debtor-in-possession borrowings outstanding. + References No definition available. + Details
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- Definition Amount of letters of credit outstanding under debtor-in-possession financing arrangement. + References No definition available. + Details
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- Definition Amount of reorganization items related to debtor-in-possession facility financing costs. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=116635682&loc=d3e55730-112764 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 55 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56145-112766 + Details
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- Definition Amount of write-off of debt issuance costs and debt discounts related to prepetition debt obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 55 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56145-112766 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 852 -SubTopic 10 -Section 45 -Paragraph 9 -URI http://asc.fasb.org/extlink&oid=116635682&loc=d3e55730-112764 + Details
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- Definition Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12355-112629 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 470 -SubTopic 50 -Section 40 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=117329964&loc=d3e12317-112629 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585 + Details
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- Definition The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(22)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(16)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(16)) -URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910 + Details
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- Definition The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used. + References No definition available. + Details
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- Definition Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 + Details
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- Definition The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3291-108585 + Details
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