Derivative Instruments - Fair value of derivative instruments not designated as hedging (Details) - Natural gas swaps - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Assets:
Fair value of assets	$ 173,946	$ 63,994
Other current assets
Assets:
Fair value of assets	74,299	23,596
Other deferred charges
Assets:
Fair value of assets	99,647	40,398
Other current liabilities
Liabilities:
Fair value of liabilities	0	0
Other deferred credits
Liabilities:
Fair value of liabilities	$ 0	$ 0

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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