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Common Stock - Additional Information (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Class Of Stock [Line Items] |  |  |
Preferred stock, shares outstanding | 0 | 0 |
Amount available for dividend distribution without affecting covenants | $ 311,800 |  |
Preferred stock, shares authorized | 10,000,000 |  |
Proceeds from issuance of common stock | $ 72,200 | $ 64,573 | $ 1,207
Common stock, shares authorized | 200,000,000 | 200,000,000 |
Common Stock [Member] |  |  |
Class Of Stock [Line Items] |  |  |
Shares issued through sales agency agreements | 1,905,000 | 1,409,588 |
Issuance of common stock through sales agency agreements, net of issuance costs | $ 70,561 | $ 63,571 |
Sales Agency Agreement [Member] |  |  |
Class Of Stock [Line Items] |  |  |
Common stock, shares authorized | 3,200,000 |  |
Common stock shares authorized under sales agency agreements remaining shares authorized to sell | 1,300,000 |  |
Avista Utilities [Member] |  |  |
Class Of Stock [Line Items] |  |  |
Regulatory restrictions, maximum debt to equity | 35.00% |  |

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