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Regulatory Matters - Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2021 | Dec. 31, 2020
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | $ 652,603 |
Not earning a return, asset | 193,618 |
Pending regulatory treatment, asset | 58,188 |
Regulatory assets | 43,783 | $ 13,673
Non-current regulatory assets | 860,626 | 750,443
Earning a return, liability | 738,730 |
Not earning a return, liability | 42,099 |
Pending Regulatory Treatment Liability | 157,835 |
Regulatory liabilities | 77,149 | 46,435
Non-current regulatory liabilities | 861,515 | 784,820
Natural Gas Deferrals [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, liability | 0 |
Not earning a return, liability | 0 |
Pending Regulatory Treatment Liability | 0 |
Regulatory liabilities | 0 | 874
Non-current regulatory liabilities | 0 | 0
Deferred Power Costs [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, liability | 11,891 |
Not earning a return, liability | 0 |
Pending Regulatory Treatment Liability | 0 |
Regulatory liabilities | 6,457 | 20,299
Non-current regulatory liabilities | 5,434 | 17,570
Utility Plant Retirement Costs [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, liability | 350,190 |
Not earning a return, liability | 0 |
Pending Regulatory Treatment Liability | 0 |
Regulatory liabilities | 0 | 0
Non-current regulatory liabilities | 350,190 | 325,832
Income Tax Related Liabilities [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, liability | 346,847 |
Not earning a return, liability | 24,411 |
Pending Regulatory Treatment Liability | 143,862 |
Regulatory liabilities | 56,331 | 14,952
Non-current regulatory liabilities | 458,789 | 399,677
Interest Rate Swaps [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, liability | 13,589 |
Not earning a return, liability | 0 |
Pending Regulatory Treatment Liability | 1,473 |
Regulatory liabilities | 0 | 0
Non-current regulatory liabilities | $ 15,062 | 15,046
Decoupling Rebates [Member] |  |
Regulated Asset Liability [Line Items] |  |
Remaining amortization period, regulatory liability | 1 year |
Earning a return, liability | $ 9,308 |
Not earning a return, liability | 0 |
Pending Regulatory Treatment Liability | 0 |
Regulatory liabilities | 3,049 | 1,447
Non-current regulatory liabilities | 6,259 | 1,519
COVID-19 Deferrals [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, liability | 0 |
Not earning a return, liability | 0 |
Pending Regulatory Treatment Liability | 12,500 |
Regulatory liabilities | 0 | 0
Non-current regulatory liabilities | 12,500 | 10,949
Other Regulatory Liabilities [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, liability | 6,905 |
Not earning a return, liability | 17,688 |
Pending Regulatory Treatment Liability | 0 |
Regulatory liabilities | 11,312 | 8,863
Non-current regulatory liabilities | 13,281 | 14,227
Deferred Income Tax [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 244,154 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 0 | 0
Non-current regulatory assets | 244,154 | 108,517
Pension and Other Postretirement Benefit Plans [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 0 |
Not earning a return, asset | 165,696 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 0 | 0
Non-current regulatory assets | 165,696 | 198,746
Energy commodity derivatives |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 0 |
Not earning a return, asset | 15,385 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 12,447 | 2,073
Non-current regulatory assets | 2,938 | 5,722
Unamortized Debt Repurchase Costs [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 6,768 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 0 | 0
Non-current regulatory assets | $ 6,768 | 7,512
Settlement with Coeur d'Alene Tribe [Member] |  |
Regulated Asset Liability [Line Items] |  |
Remaining amortization period, regulatory assets | 38 years |
Earning a return, asset | $ 38,926 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 0 | 0
Non-current regulatory assets | 38,926 | 40,043
Demand Side Management Programs [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 0 |
Not earning a return, asset | 3,974 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 0 | 0
Non-current regulatory assets | $ 3,974 | 3,814
Decoupling Surcharge [Member] |  |
Regulated Asset Liability [Line Items] |  |
Remaining amortization period, regulatory assets | 2 years |
Earning a return, asset | $ 24,532 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 9,907 | 7,123
Non-current regulatory assets | 14,625 | 17,123
Utility Plant to be Abandoned [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 26,771 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 0 | 0
Non-current regulatory assets | 26,771 | 28,916
Interest Rate Swaps [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 158,082 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 41,672 |
Regulatory assets | 0 | 0
Non-current regulatory assets | 199,754 | 214,851
Deferred power costs [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 10,835 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 7,334 | 1,775
Non-current regulatory assets | 3,501 | 1,562
Deferred Natural Gas Costs [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 21,027 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 14,095 | 2,308
Non-current regulatory assets | 6,932 | 0
AFUDC Above FERC Allowed Rate [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 48,455 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 0 | 0
Non-current regulatory assets | 48,455 | 47,393
COVID-19 Deferrals [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 0 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 13,591 |
Regulatory assets | 0 | 0
Non-current regulatory assets | 13,591 | 8,166
Advanced Meter Infrastructure [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 36,008 |
Not earning a return, asset | 0 |
Pending regulatory treatment, asset | 0 |
Regulatory assets | 0 | 0
Non-current regulatory assets | 36,008 | 26,379
Other Regulatory Assets [Member] |  |
Regulated Asset Liability [Line Items] |  |
Earning a return, asset | 37,045 |
Not earning a return, asset | 8,563 |
Pending regulatory treatment, asset | 2,925 |
Regulatory assets | 0 | 394
Non-current regulatory assets | $ 48,533 | $ 41,699

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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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