Derivative Instruments - Assets and liabilities (Details) - Commodity derivative - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Commodity derivative assets
Gross amounts on balance sheet	$ 782,629	$ 882,817
Gross amounts offset on balance sheet	(157,656)	(126,794)
Total asset derivatives	624,973	756,023
Commodity derivative liabilities
Gross amounts on balance sheet	(163,866)	(137,034)
Gross amounts offset on balance sheet	157,656	126,794
Total liability derivatives	$ (6,210)	$ (10,240)

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