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Summary of Significant Accounting Policies - Estimated Retirement Costs Collected from Customers (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Regulated Asset Liability [Line Items]
Regulatory liability for utility plant retirement costs	$ 861,515	$ 784,820
Utility Plant Retirement Costs [Member]
Regulated Asset Liability [Line Items]
Regulatory liability for utility plant retirement costs	$ 350,190	$ 325,832

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- Definition

Regulated Asset Liability [Line Items]

+ References

No definition available.

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- Definition

The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

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