Asset retirement obligations (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Mar. 21, 2017	Dec. 31, 2017	Dec. 31, 2018
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance		$ 70,476	$ 35,990
Liabilities incurred in current period		2,498	689
Liabilities settled and disposed in current period		(44,097)	(17,868)
Revisions in estimated cash flows		4,248	2,452
Accretion expense		2,865	1,884
Ending balance	$ 70,476	35,990	23,147
Fair value fresh-start adjustment	(2,757)
Less current portion included in accounts payable and accrued liabilities			1,057
Asset retirement obligations, long-term	64,216	33,216	$ 22,090
Predecessor
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning balance	72,137	$ 73,233
Liabilities incurred in current period	535
Liabilities settled and disposed in current period	(869)
Revisions in estimated cash flows	181
Accretion expense	1,249
Ending balance	73,233
Asset retirement obligations, long-term	$ 66,973

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
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Current portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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Amount of asset retirement obligations incurred during the period.

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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Noncurrent portion of the carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

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Total fresh-start adjustment to liabilities.

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-Publisher FASB
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