Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Current Assets:
Cash and Cash Equivalents	$ 11.2	$ 8.4	$ 14.3
Accounts Receivable, net	85.9us-gaap_AccountsReceivableNetCurrent	60.7us-gaap_AccountsReceivableNetCurrent	69.5us-gaap_AccountsReceivableNetCurrent
Accrued Revenue	64.2us-gaap_UnbilledContractsReceivable	48.5us-gaap_UnbilledContractsReceivable	49.6us-gaap_UnbilledContractsReceivable
Exchange Gas Receivable	4.0us-gaap_OtherReceivablesNetCurrent	15.0us-gaap_OtherReceivablesNetCurrent	1.3us-gaap_OtherReceivablesNetCurrent
Deferred Income Taxes	2.6us-gaap_DeferredTaxAssetsNetCurrent
Gas Inventory	0.4	1.1	0.6
Materials and Supplies	5.9	6.3	5.1
Prepayments and Other	5.9us-gaap_PrepaidExpenseAndOtherAssets	5.2us-gaap_PrepaidExpenseAndOtherAssets	5.2us-gaap_PrepaidExpenseAndOtherAssets
Total Current Assets	180.1us-gaap_AssetsCurrent	145.2us-gaap_AssetsCurrent	145.6us-gaap_AssetsCurrent
Utility Plant:
Gas	529.7	522.9	483.0
Electric	393.7	390.6	377.3
Common	34.6	32.7	31.6
Construction Work in Progress	39.4	42.6	21.3
Total Utility Plant	997.4	988.8	913.2
Less: Accumulated Depreciation	259.2	255.1	246.4
Net Utility Plant	738.2	733.7	666.8
Other Noncurrent Assets:
Regulatory Assets	106.2us-gaap_RegulatoryAssetsNoncurrent	107.6us-gaap_RegulatoryAssetsNoncurrent	96.5us-gaap_RegulatoryAssetsNoncurrent
Other Assets	16.3us-gaap_OtherAssetsNoncurrent	13.7us-gaap_OtherAssetsNoncurrent	19.1us-gaap_OtherAssetsNoncurrent
Total Other Noncurrent Assets	122.5us-gaap_AssetsNoncurrent	121.3us-gaap_AssetsNoncurrent	115.6us-gaap_AssetsNoncurrent
TOTAL ASSETS	1,040.8us-gaap_Assets	1,000.2us-gaap_Assets	928.0us-gaap_Assets
Current Liabilities:
Accounts Payable	34.8us-gaap_AccountsPayableCurrent	44.2us-gaap_AccountsPayableCurrent	31.8us-gaap_AccountsPayableCurrent
Short-Term Debt	32.0us-gaap_ShortTermBorrowings	29.3us-gaap_ShortTermBorrowings	59.2us-gaap_ShortTermBorrowings
Long-Term Debt, Current Portion	4.0us-gaap_LongTermDebtCurrent	4.0us-gaap_LongTermDebtCurrent	2.5us-gaap_LongTermDebtCurrent
Energy Supply Obligations	12.6	22.1	6.1
Deferred Income Taxes		3.1us-gaap_DeferredTaxLiabilitiesCurrent	3.4us-gaap_DeferredTaxLiabilitiesCurrent
Environmental Obligations	3.4	3.5	1.4
Interest Payable	6.3us-gaap_InterestPayableCurrent	3.5us-gaap_InterestPayableCurrent	5.4us-gaap_InterestPayableCurrent
Regulatory Liabilities (Note 6)	39.4us-gaap_RegulatoryLiabilityCurrent	8.7us-gaap_RegulatoryLiabilityCurrent	13.1us-gaap_RegulatoryLiabilityCurrent
Other Current Liabilities	7.9us-gaap_OtherLiabilitiesCurrent	11.0us-gaap_OtherLiabilitiesCurrent	8.8us-gaap_OtherLiabilitiesCurrent
Total Current Liabilities	140.4us-gaap_LiabilitiesCurrent	129.4us-gaap_LiabilitiesCurrent	131.7us-gaap_LiabilitiesCurrent
Noncurrent Liabilities:
Deferred Income Taxes	87.3	72.9	82.5
Cost of Removal Obligations	65.7	63.8	59.2
Retirement Benefit Obligations	121.4	118.6	79.1
Capital Lease Obligations	8.2	7.5	0.1
Energy Supply Obligations	1.9	1.9	2.3
Environmental Obligations	2.0	2.0	12.8
Other Noncurrent Liabilities	1.9us-gaap_OtherLiabilitiesNoncurrent	1.9us-gaap_OtherLiabilitiesNoncurrent	1.6us-gaap_OtherLiabilitiesNoncurrent
Total Noncurrent Liabilities	288.4us-gaap_LiabilitiesNoncurrent	268.6us-gaap_LiabilitiesNoncurrent	237.6us-gaap_LiabilitiesNoncurrent
Capitalization:
Long-Term Debt, Less Current Portion	328.7us-gaap_LongTermDebtNoncurrent	328.9us-gaap_LongTermDebtNoncurrent	284.7us-gaap_LongTermDebtNoncurrent
Stockholders' Equity:
Common Equity (Authorized: 25,000,000 and Outstanding:13,966,150, 13,886,768 and 13,916,026 Shares)	236.0us-gaap_CommonStockValue	234.7us-gaap_CommonStockValue	233.1us-gaap_CommonStockValue
Retained Earnings	47.1	38.4	40.7
Total Common Stock Equity	283.1utl_CommonStockEquity	273.1utl_CommonStockEquity	273.8utl_CommonStockEquity
Preferred Stock	0.2us-gaap_PreferredStockValue	0.2us-gaap_PreferredStockValue	0.2us-gaap_PreferredStockValue
Total Stockholders' Equity	283.3us-gaap_StockholdersEquity	273.3us-gaap_StockholdersEquity	274.0us-gaap_StockholdersEquity
Total Capitalization	612.0	602.2	558.7
Commitments and Contingencies (Notes 6 & 7)
TOTAL LIABILITIES AND CAPITALIZATION	$ 1,040.8	$ 1,000.2	$ 928.0

Carrying value as of the balance sheet date of liabilities incurred (and for which invoices have typically been received) and payable to vendors for goods and services received that are used in an entity's business. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

Name:	us-gaap_AccountsPayableCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant