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Allowance for Doubtful Accounts (Tables) | 12 Months Ended
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Dec. 31, 2017
Allowance for Doubtful Accounts | The following table shows the balances and activity in the Company’s Allowance for Doubtful Accounts for 2015—2017 (millions): ALLOWANCE FOR DOUBTFUL ACCOUNTS
|  | Balance at Beginning of Period |  |  | Provision |  |  | Recoveries |  |  | Accounts Written Off |  |  | Balance at End of Period |
Year Ended December 31, 2017 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric |  | $ | 0.8 |  |  | $ | 1.8 |  |  | $ | 0.3 |  |  | $ | 2.0 |  |  | $ | 0.9 |
Gas |  |  | 0.2 |  |  |  | 1.9 |  |  |  | 0.3 |  |  |  | 1.8 |  |  |  | 0.6 |
Other |  |  | 0.1 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 0.1 |
|  | $ | 1.1 |  |  | $ | 3.7 |  |  | $ | 0.6 |  |  | $ | 3.8 |  |  | $ | 1.6 |
Year Ended December 31, 2016 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric |  | $ | 0.6 |  |  | $ | 2.9 |  |  | $ | 0.3 |  |  | $ | 3.0 |  |  | $ | 0.8 |
Gas |  |  | 0.5 |  |  |  | 1.7 |  |  |  | 0.3 |  |  |  | 2.3 |  |  |  | 0.2 |
Other |  |  | 0.1 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 0.1 |
|  | $ | 1.2 |  |  | $ | 4.6 |  |  | $ | 0.6 |  |  | $ | 5.3 |  |  | $ | 1.1 |
Year Ended December 31, 2015 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Electric |  | $ | 1.3 |  |  | $ | 2.5 |  |  | $ | 0.3 |  |  | $ | 3.5 |  |  | $ | 0.6 |
Gas |  |  | 0.4 |  |  |  | 2.8 |  |  |  | 0.4 |  |  |  | 3.1 |  |  |  | 0.5 |
Other |  |  | 0.1 |  |  |  | — |  |  |  | — |  |  |  | — |  |  |  | 0.1 |
|  | $ | 1.8 |  |  | $ | 5.3 |  |  | $ | 0.7 |  |  | $ | 6.6 |  |  | $ | 1.2 |

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