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Balance Sheet Components Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands | Sep. 30, 2019 | Dec. 31, 2018
--- | --- | ---
Regulated Asset Liability [Line Items] |  |
Regulatory assets | $ 19,890 | $ 48,552
Regulatory Assets, Noncurrent | 688,814 | 614,354
Regulatory liabilities | 43,442 | 113,209
Non-current regulatory liabilities | 786,131 | 780,701
Income Tax Related |  |
Regulated Asset Liability [Line Items] |  |
Regulatory liabilities | 23,409 | 27,997
Non-current regulatory liabilities | 414,857 | 425,613
Natural Gas Deferrals [Member] |  |
Regulated Asset Liability [Line Items] |  |
Regulatory liabilities | 3,762 | 40,713
Non-current regulatory liabilities | 0 | 0
Power Deferrals Regulatory Liability [Member] |  |
Regulated Asset Liability [Line Items] |  |
Regulatory liabilities | 7,711 | 25,072
Non-current regulatory liabilities | 29,618 | 16,933
Decoupling surcharge |  |
Regulated Asset Liability [Line Items] |  |
Regulatory liabilities | 99 | 6,782
Non-current regulatory liabilities | 3,098 | 204
Removal Costs [Member] |  |
Regulated Asset Liability [Line Items] |  |
Regulatory liabilities | 0 | 0
Non-current regulatory liabilities | 307,923 | 297,379
Interest rate swaps |  |
Regulated Asset Liability [Line Items] |  |
Regulatory liabilities | 0 | 0
Non-current regulatory liabilities | 16,863 | 28,078
Other Regulatory Assets (Liabilities) [Member] |  |
Regulated Asset Liability [Line Items] |  |
Regulatory liabilities | 8,461 | 12,645
Non-current regulatory liabilities | 13,772 | 12,494
Energy commodity derivatives |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 6,374 | 41,428
Regulatory Assets, Noncurrent | 1,018 | 16,866
Decoupling surcharge |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 10,266 | 3,408
Regulatory Assets, Noncurrent | 18,395 | 17,501
Pension and other postretirement benefit plans |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 0 | 0
Regulatory Assets, Noncurrent | 218,006 | 228,062
Interest rate swaps |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 0 | 0
Regulatory Assets, Noncurrent | 189,872 | 133,854
Income Tax Related |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 0 | 0
Regulatory Assets, Noncurrent | 93,818 | 91,188
Settlement with Coeur d'Alene Tribe |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 0 | 0
Regulatory Assets, Noncurrent | 41,660 | 42,643
AFUDC above FERC allowed rate (1) |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 0 | 0
Regulatory Assets, Noncurrent | 37,239 | 1,814
Demand side management programs |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 0 | 0
Regulatory Assets, Noncurrent | 11,701 | 19,674
Utility plant to be abandoned |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 0 | 0
Regulatory Assets, Noncurrent | 25,849 | 24,334
Other Regulatory Assets (Liabilities) [Member] |  |
Regulated Asset Liability [Line Items] |  |
Regulatory assets | 3,250 | 3,716
Regulatory Assets, Noncurrent | $ 51,256 | $ 38,418

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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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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current 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 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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