Derivative instruments (Derivative instruments recorded on the balance sheet at fair value) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Mar. 21, 2017
Fair value of derivative instruments
Derivative assets, gross	$ 29,622	$ 1,332
Derivative liabilities, gross	(4,940)	(14,458)
Derivative assets (liabilities), net	24,682	(13,126)
Netting adjustments, assets	(3,398)	1,332
Netting adjustments, liabilities	3,398	(1,332)
Current derivative assets, net	24,025	0	$ 19,058
Current derivative liabilities, net	0	(8,959)
Current derivative assets (liabilities), net	24,025	(8,959)
Long-term derivative assets, net	2,199	0	14,295
Long-term derivative liabilities, net	(1,542)	(4,167)
Long-term derivative assets (liabilities), net	657	(4,167)
Predecessor
Fair value of derivative instruments
Current derivative assets, net			19,058
Long-term derivative assets, net			$ 14,295
Natural gas derivative contracts
Fair value of derivative instruments
Derivative assets, gross	833	1,332
Derivative liabilities, gross	(488)	(1,054)
Derivative assets (liabilities), net	345	278
NGL derivative contracts
Fair value of derivative instruments
Derivative assets, gross	4,581	0
Derivative liabilities, gross	0	0
Derivative assets (liabilities), net	4,581	0
Crude oil derivative contracts
Fair value of derivative instruments
Derivative assets, gross	24,208	0
Derivative liabilities, gross	(4,452)	(13,404)
Derivative assets (liabilities), net	$ 19,756	$ (13,404)

Derivative Asset (Liability), Net, Current

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Fair value of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, not subject to a master netting arrangement, deducted from derivative assets.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset, expected to be settled within one year or normal operating cycle, if longer. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

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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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