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Asset Retirement Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	$ 64,205	$ 56,800
Liabilities Incurred	5,999	3,445
Liabilities Settled	(317)	(380)
Accretion	2,769	2,741
Revisions to Prior Estimates	(1,225)	1,599
Ending Balance	71,431	64,205
Electric Utilities
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	9,329	6,258
Liabilities Incurred	1,217	0
Liabilities Settled	0	0
Accretion	407	385
Revisions to Prior Estimates	0	2,686
Ending Balance	10,953	9,329
Gas Utilities
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	36,085	34,627
Liabilities Incurred	4,782	0
Liabilities Settled	(132)	0
Accretion	1,539	1,458
Revisions to Prior Estimates	0	0
Ending Balance	42,274	36,085
Power Generation
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	4,739	300
Liabilities Incurred	0	3,445
Liabilities Settled	0	0
Accretion	206	158
Revisions to Prior Estimates	0	836
Ending Balance	4,945	4,739
Mining
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Beginning Balance	14,052	15,615
Liabilities Incurred	0	0
Liabilities Settled	(185)	(380)
Accretion	617	740
Revisions to Prior Estimates	(1,225)	(1,923)
Ending Balance	$ 13,259	$ 14,052

X

- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
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- Definition

Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
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Amount of asset retirement obligations incurred during the period.

+ References

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Amount of asset retirement obligations settled, or otherwise disposed of, during the period. This may include asset retirement obligations transferred to third parties associated with the sale of a long-lived asset.

+ References

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- Definition

Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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