Derivative Instruments - Realized and unrealized gains and (losses) on derivative instruments (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Gains and (losses) on derivative instruments
Net unrealized gains on derivative instruments	$ 173,946		$ 63,994
Natural gas swaps \| Regulatory liability
Gains and (losses) on derivative instruments
Net unrealized gains on derivative instruments	173,946		$ 63,994
Natural gas swaps \| Fuel
Gains and (losses) on derivative instruments
Gains	8,078	$ 101
Losses	(79)	(1,244)
Total	$ 7,999	$ (1,143)

Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

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Amount of increase in the fair value of derivatives recognized in the income statement.

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
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Amount of decrease in the fair value of derivatives recognized in the income statement.

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The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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-Publisher FASB
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