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Number Of Cogeneration Facilities

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Amount of amortization expense attributable to debt issuance costs.

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Capitalized costs of unproved properties incurred for any combination mineral interests acquisitions and other costs not previously disclosed within this table.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Amount of deferred cost, excluding capitalized cost related to contract with customer; classified as noncurrent.

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Sum of the carrying amounts as of the balance sheet date of deferred costs capitalized at the end of the reporting period that are expected to be charged against earnings within one year or the normal operating cycle, if longer.

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Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of cash restricted as to withdrawal or usage, classified as current. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

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Amount of cash restricted as to withdrawal or usage, classified as noncurrent. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Basis of Presentation and Significant Accounting Policies - Narrative (Details)	2 Months Ended	7 Months Ended	9 Months Ended	10 Months Ended	12 Months Ended
	Feb. 28, 2017 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($) facility	Dec. 31, 2017 USD ($) facility	Dec. 31, 2016 USD ($)
Public Utilities, General Disclosures [Line Items]
Restricted cash, current				$ 35,000,000	$ 35,000,000
Restricted cash, noncurrent	$ 125,000			0	0
Net deferred financing fees, noncurrent				20,000,000	20,000,000
Amortization of debt issuance costs		$ 926,000	$ 4,042,000	1,988,000
Net capitalized costs attributable to unproved properties				$ 517,000,000	$ 517,000,000
Number of cogeneration facilities \| facility				5	5
Largest customers \| Sales \| Oil, natural gas and NGL sales \| Customer one
Public Utilities, General Disclosures [Line Items]
Concentration risk				37.00%
Largest customers \| Sales \| Oil, natural gas and NGL sales \| Customer two
Public Utilities, General Disclosures [Line Items]
Concentration risk				34.00%
Largest customers \| Sales \| Oil, natural gas and NGL sales \| Customer three
Public Utilities, General Disclosures [Line Items]
Concentration risk				15.00%
Largest customers \| Sales \| Electricity sales \| Two Customers [Member]
Public Utilities, General Disclosures [Line Items]
Concentration risk					100.00%
Largest customers \| Trade accounts receivable \| Customer one
Public Utilities, General Disclosures [Line Items]
Concentration risk				35.00%
Largest customers \| Trade accounts receivable \| Customer two
Public Utilities, General Disclosures [Line Items]
Concentration risk				26.00%
Buildings and leasehold improvements \| Minimum
Public Utilities, General Disclosures [Line Items]
Expected useful life				10 years
Buildings and leasehold improvements \| Maximum
Public Utilities, General Disclosures [Line Items]
Expected useful life				39 years
Plant and pipeline, drilling and other equipment \| Minimum
Public Utilities, General Disclosures [Line Items]
Expected useful life				2 years
Plant and pipeline, drilling and other equipment \| Maximum
Public Utilities, General Disclosures [Line Items]
Expected useful life				30 years
Predecessor
Public Utilities, General Disclosures [Line Items]
Restricted cash, noncurrent						$ 197,793,000
Net deferred financing fees, current						6,000,000
Amortization of debt issuance costs	$ 416,000					1,849,000
Net capitalized costs attributable to unproved properties						680,000,000
Impairment charges with unproved oil and natural gas properties						$ 13,000,000
Predecessor \| Largest customers \| Sales \| Oil, natural gas and NGL sales \| Customer one
Public Utilities, General Disclosures [Line Items]
Concentration risk	36.00%					34.00%
Predecessor \| Largest customers \| Sales \| Oil, natural gas and NGL sales \| Customer two
Public Utilities, General Disclosures [Line Items]
Concentration risk	31.00%					28.00%
Predecessor \| Largest customers \| Sales \| Electricity sales \| Two Customers [Member]
Public Utilities, General Disclosures [Line Items]
Concentration risk						100.00%
Predecessor \| Largest customers \| Trade accounts receivable \| Customer one
Public Utilities, General Disclosures [Line Items]
Concentration risk						29.00%
Predecessor \| Largest customers \| Trade accounts receivable \| Customer two
Public Utilities, General Disclosures [Line Items]
Concentration risk						21.00%
Interest Expense
Public Utilities, General Disclosures [Line Items]
Amortization of debt issuance costs				$ 2,000,000
Interest Expense \| Predecessor
Public Utilities, General Disclosures [Line Items]
Amortization of debt issuance costs	$ 0					$ 2,000,000
Restricted Stock Units (RSUs)
Public Utilities, General Disclosures [Line Items]
Vesting period			3 years	3 years
Performance-based Restricted Stock Units (PRSUs)
Public Utilities, General Disclosures [Line Items]
Vesting period				3 years