Derivative Instruments - Assets and liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Commodity derivative assets
Gross amounts on balance sheet	$ 1,326,727	$ 1,914,245
Gross amounts offset on balance sheet	(150,638)	(110,160)
Total asset derivatives	1,176,089	1,804,085
Commodity derivative liabilities
Gross amounts on balance sheet	(4,823)	(324,667)
Gross amounts offset on balance sheet	111	120,798
Total liability derivatives	$ (4,712)	$ (203,869)

Fair value of liability associated with 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.

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