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Utility Plant Intangible Assets - Schedule of Finite-Lived Intangible Assets (Details) - USD ($) $ in Thousands | Dec. 31, 2020 | Jan. 08, 2020 | Dec. 31, 2019
--- | --- | --- | ---
Finite-Lived Intangible Assets [Line Items] |  |  |
Intangible assets | $ 35,167 |  | $ 33,424
Purchase premium customer relationships | 13,400 |  | 13,400
Net intangible assets | 21,270 |  | 20,245
Concession fees |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Intangible assets | 6,800 | $ 5,000 | 6,800
Accumulated amortization of intangible assets | 6,324 |  | 6,052
Purchase premium customer relationships |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Intangible assets | 1,400 |  |
Accumulated amortization of intangible assets | 1,094 |  | 201
Other intangibles |  |  |
Finite-Lived Intangible Assets [Line Items] |  |  |
Intangible assets | 14,967 |  | 13,224
Accumulated amortization of intangible assets | $ 6,479 |  | $ 6,926

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