Derivative Instruments - Fair value (Details) $ in Thousands	Mar. 31, 2020 USD ($) item	Dec. 31, 2019 USD ($) item
Fair value of derivative instruments
Current portion of fair value of derivative assets	$ 816,444	$ 422,849
Noncurrent portion of fair value of derivative assets	284,461	333,174
Current portion of fair value of derivative liabilities		6,721
Noncurrent portion of fair value of derivative liabilities	215	3,519
Commodity derivative
Fair value of derivative instruments
Total asset derivatives	1,100,905	756,023
Total liability derivatives	215	10,240
Derivatives not designated as hedges for accounting purposes
Fair value of derivative instruments
Total asset derivatives	1,100,905	756,023
Total liability derivatives	215	10,240
Net derivatives	1,100,690	745,783
Derivatives not designated as hedges for accounting purposes \| Commodity derivative
Fair value of derivative instruments
Current portion of fair value of derivative assets	816,444	422,849
Noncurrent portion of fair value of derivative assets	284,461	333,174
Current portion of fair value of derivative liabilities		6,721
Noncurrent portion of fair value of derivative liabilities	$ 215	$ 3,519
Derivatives designated as hedges for accounting purposes
Fair value of derivative instruments
Number of derivative instruments held designated as hedges \| item	0	0

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. 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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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 after one year or the 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 value, after the effects of master netting arrangements, of a financial liability or 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. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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The number of derivative instruments of a particular group held by the entity.

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