Derivative instruments (Non-hedge derivative gains (losses) in the consolidated statements of operations) (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended	12 Months Ended
Mar. 21, 2017	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2016
Derivative Gains (Losses) [Line Items]
Change in fair value of commodity price derivatives		$ (46,478)	$ 37,807
Settlement (losses) gains on commodity price derivatives		15,676	(18,510)
Settlement gains on early terminations of commodity price derivatives		0	0
Non-hedge derivative (losses) gains		$ (30,802)	$ 19,297
Predecessor
Derivative Gains (Losses) [Line Items]
Change in fair value of commodity price derivatives	$ 46,721			$ (176,607)
Settlement (losses) gains on commodity price derivatives	1,285			62,626
Settlement gains on early terminations of commodity price derivatives	0			91,144
Non-hedge derivative (losses) gains	$ 48,006			$ (22,837)

Derivative instruments not designated as hedging instruments gain loss from early terminations of commodity contract.

No definition available.

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- Definition

Derivative instruments not designated as hedging instruments gain loss from settlement of commodity contracts.

+ References

No definition available.

+ Details

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- Definition

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.

+ References

No definition available.

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- Definition

Amount of realized and unrealized gain (loss) of derivative instruments not designated or qualifying as hedging instruments.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CC
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998890-113959

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959

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- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of open agreements to purchase or sell mineral resources, energy, and agricultural products at some future point held at each balance sheet date, that was included in earnings for the period.

+ References

Reference 1: 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=109223946&loc=d3e3602-108585

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