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Regulatory Matters (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Regulated Asset Liability [Line Items] |  |
Company Share of Benefit (Expense) Under Washington Energy Recovery Mechanism | $ 4,400 | $ 6,100
Threshold to Return Washington Energy Recovery Mechanism Dollars to Customers | 30,000 |
Deferred natural gas costs | $ 3,200 | 40,700
WASHINGTON |  |
Regulated Asset Liability [Line Items] |  |
Decoupling Maximum Rate Increase Request | 3.00% |
Power Deferrals [Member] | WASHINGTON |  |
Regulated Asset Liability [Line Items] |  |
Regulatory Liabilities | $ (37,000) | (34,400)
Power Deferrals [Member] | IDAHO |  |
Regulated Asset Liability [Line Items] |  |
Regulatory Liabilities |  | (7,600)
Revenue Subject to Refund [Member] | WASHINGTON |  |
Regulated Asset Liability [Line Items] |  |
Regulatory Liabilities | 0 | (693)
Revenue Subject to Refund [Member] | IDAHO |  |
Regulated Asset Liability [Line Items] |  |
Regulatory Liabilities | $ (686) | $ (774)

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