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Allowance for Doubtful Accounts (Tables) | 12 Months Ended
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Dec. 31, 2024
Allowance For Doubtful Accounts [Abstract] |
Allowance for Doubtful Accounts | The following table shows the balances and activity in the Company’s Allowance for Doubtful Accounts for 2024, 2023 and 2022 (millions): ALLOWANCE FOR DOUBTFUL ACCOUNTS
|  | Balance at Beginning of Period |  |  | Provision |  |  | Recoveries |  |  | Accounts Written Off |  |  | Regulatory Deferrals |  |  | Balance at End of Period |
Year Ended December 31, 2024 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric |  | $ | 1.5 |  |  | $ | 2.0 |  |  | $ | 0.2 |  |  | $ | 2.3 |  |  | $ | — |  |  | $ | 1.4 |
Gas |  |  | 0.9 |  |  |  | 2.3 |  |  |  | 0.3 |  |  |  | 2.5 |  |  |  | — |  |  |  | 1.0 |
|  | $ | 2.4 |  |  | $ | 4.3 |  |  | $ | 0.5 |  |  | $ | 4.8 |  |  | $ | — |  |  | $ | 2.4 |
Year Ended December 31, 2023 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric |  | $ | 1.6 |  |  | $ | 3.6 |  |  | $ | 0.2 |  |  | $ | 3.9 |  |  | $ | — |  |  | $ | 1.5 |
Gas |  |  | 1.0 |  |  |  | 2.8 |  |  |  | 0.4 |  |  |  | 3.3 |  |  |  | — |  |  |  | 0.9 |
|  | $ | 2.6 |  |  | $ | 6.4 |  |  | $ | 0.6 |  |  | $ | 7.2 |  |  | $ | — |  |  | $ | 2.4 |
Year Ended December 31, 2022 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric |  | $ | 2.0 |  |  | $ | 4.2 |  |  | $ | 0.3 |  |  | $ | 4.4 |  |  | $ | (0.5 | ) |  | $ | 1.6 |
Gas |  |  | 1.3 |  |  |  | 2.5 |  |  |  | 0.6 |  |  |  | 3.2 |  |  |  | (0.2 | ) |  |  | 1.0 |
|  | $ | 3.3 |  |  | $ | 6.7 |  |  | $ | 0.9 |  |  | $ | 7.6 |  |  | $ | (0.7 | ) |  | $ | 2.6 |

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- Definition Allowance For Doubtful Accounts Abstract + References No definition available. + Details
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Namespace Prefix: | utl_
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- Definition Allowance for Doubtful Accounts, Table. + References No definition available. + Details
Name: | utl_AllowanceForDoubtfulAccountsTableTextBlockTableTextBlock
Namespace Prefix: | utl_
Data Type: | dtr-types:textBlockItemType
Balance Type: | na
Period Type: | duration