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Selected Balance Sheet Information: Materials and Supplies (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
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Selected Balance Sheet Information [Abstract] |  |
Materials and supplies | $ 85,612 | $ 85,250
Fuel - Electric Utilities | 1,240 | 1,531
Natural gas in storage | 58,891 | 30,619
Total materials, supplies and fuel | $ 145,743 | $ 117,400

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