Derivatives (Fair Value of Commodity Derivatives with Cash Collateral) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Estimated fair value of Company's commodity derivative instruments for cash collateral and associated cash as collateral
Net derivative asset position, Collateral paid	$ 208,670	$ 56,005
Commodity derivative assets	(157,301)	(10,323)
Net derivative asset position, net	$ 51,369	$ 45,682

Fair value, after offset of derivative liability, 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, before offset against an obligation to return collateral under a master netting arrangement. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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