Energy Supply	12 Months Ended
Dec. 31, 2011
Energy Supply [Abstract]
Energy Supply	Note 4: Energy Supply Natural Gas Supply Unitil manages gas supply for customers served by Northern Utilities in Maine and New Hampshire as well as customers served by Fitchburg in Massachusetts. Fitchburg's residential and C&I business customers have the opportunity to purchase their natural gas supply from third-party gas supply vendors. Many large and some medium C&I customers purchase their supplies from third-party suppliers, while most of Fitchburg's residential and small C&I customers continue to purchase their supplies at regulated rates from Fitchburg. Northern Utilities' C&I customers have the opportunity to purchase their natural gas supply from third-party gas supply vendors, and third-party supply is prevalent among Northern Utilities' larger C&I customers. Most small C&I customers, as well as all residential customers, purchase their gas supply from Northern Utilities under regulated rates and tariffs. The approved costs associated with the acquisition of such wholesale natural gas supplies for customers who do not contract with third-party suppliers are recovered on a pass-through basis through periodically-adjusted rates and are included in Purchased Gas in the Consolidated Statements of Earnings. On November 2, 2011, the Massachusetts Supreme Judicial Court (SJC) issued its decision vacating an order issued on November 2, 2009 by the MDPU in which the MDPU ordered the Company's electric and natural gas distribution utility, Fitchburg, to refund $4.6 million of natural gas costs, plus interest. The MDPU's original order, issued in 2009, found that Fitchburg had engaged in certain price stabilization practices for the 2007 / 2008 and 2008 / 2009 heating seasons without the MDPU's prior approval and that Fitchburg's natural gas purchasing practices were imprudent. The Company appealed the MDPU's decision to the SJC. The SJC's decision vacates the MDPU's order to refund $4.6 million, plus interest, in favor of a $0.2 million refund, plus interest. The Company had previously recorded a pre-tax charge to earnings and recognized a Regulatory Liability of $4.9 million in the fourth quarter of 2009 based on the MDPU's original order. As a result of the decision, the Regulatory Liability has been adjusted and the Company recognized a pre-tax credit of $4.7 million in the fourth quarter of 2011. This credit is recognized on the Company's 2011 Consolidated Statement of Earnings as a $4.5 million reduction in Purchased Gas expense and a reduction of $0.2 million in Interest Expense, net. Regulated Natural Gas Supply Fitchburg purchases natural gas under contracts of one year or less, as well as from producers and marketers on the spot market. Fitchburg arranges for gas delivery to its system through its own long-term contracts with Tennessee Gas Pipeline, or in the case of liquefied natural gas (LNG) or liquefied propane gas (LPG), to truck supplies to storage facilities within Fitchburg's service territory. Fitchburg has available under firm contract 14,057 MMbtu per day for transportation and underground storage capacity to its distribution facilities. As a supplement to pipeline natural gas, Fitchburg owns a propane air gas plant and a LNG storage and vaporization facility. These plants are used principally during peak load periods to augment the supply of pipeline natural gas. Northern Utilities purchases a majority of its natural gas from U.S. domestic and Canadian suppliers under contracts of one year or less, and on occasion from producers and marketers on the spot market. Northern Utilities arranges for gas delivery to its system through its own long-term contracts with various interstate pipeline and storage facilities, through peaking supply contracts delivered to its system, or in the case of LNG, to truck supplies to storage facilities within Northern Utilities' service territory. Northern Utilities has available under firm contract 100,000 MMbtu per day of year-round and seasonal transportation capacity to its distribution facilities, and 3.4 Bcf of underground storage. As a supplement to pipeline natural gas, Northern Utilities owns an LNG storage and vaporization facility. This plant is used principally during peak load periods to augment the supply of pipeline natural gas. Electric Power Supply The restructuring of the electric utility industry in New Hampshire required the divestiture of Unitil's power supply arrangements and the procurement of replacement supplies, which provided the flexibility for migration of customers to and from utility energy service. Fitchburg, Unitil Energy, and Unitil Power each are members of the New England Power Pool (NEPOOL) and participate in the ISO New England, Inc. (ISO-NE) markets for the purpose of facilitating these wholesale electric power supply transactions, which are necessary to serve Unitil's customers. As a result of restructuring of the electric utility industry in Massachusetts and New Hampshire, Unitil's customers in both New Hampshire and Massachusetts have the opportunity to purchase their electric supply from competitive third-party energy suppliers. As of December 2011, 106 or 71% of Unitil's largest New Hampshire customers, representing 25% of total New Hampshire electric energy sales, and 28 or 93% of Unitil's largest Massachusetts customers, representing 33% of total Massachusetts electric energy sales, are purchasing their electric power supply in the competitive market. Regulated Electric Power Supply In order to provide regulated electric supply service to their customers, Unitil's electric distribution utilities enter into load-following wholesale electric power supply contracts with various wholesale suppliers. Fitchburg has power supply contracts with various wholesale suppliers for the provision of Basic Service energy supply. MDPU policy dictates the pricing structure and duration of each of these contracts. Currently, all Basic Service power supply contracts for large general accounts are three months in duration and provide 100% of supply requirements. Basic Service power supply contracts for residential, small and medium general service customers are acquired every six months, are 12 months in duration and provide 50% of the supply requirements. Unitil Energy currently has power supply contracts with various wholesale suppliers for the provision of Default Service to its customers. Unitil Energy procures Default Service supply for its large general service accounts through competitive solicitations for power contracts of three months in duration for 100% of supply requirements. Unitil Energy procures Default Service supply for its other customers through a series of two one-year contracts and two two-year contracts, each providing 25% of the total supply requirements of the group. The NHPUC and MDPU regularly review alternatives to their procurement policy, which may lead to future changes in this regulated power supply procurement structure. Regional Electric Transmission and Power Markets Fitchburg, Unitil Energy and Unitil Power, as well as virtually all New England electric utilities, are participants in the ISO-NE markets. ISO-NE is the Regional Transmission Organization (RTO) in New England. The purpose of ISO-NE is to assure reliable operation of the bulk power system in the most economic manner for the region. Substantially all operation and dispatching of electric generation and bulk transmission capacity in New England is performed on a regional basis. The ISO-NE tariff imposes generating capacity and reserve obligations, and provides for the use of major transmission facilities and support payments associated therewith. The most notable benefits of the ISO-NE are coordinated power system operation in a reliable manner and a supportive business environment for the development of competitive electric markets. Electric Power Supply Divestiture In connection with the implementation of retail choice, Unitil Power, which formerly functioned as the wholesale power supply provider for Unitil Energy, and Fitchburg divested their long-term power supply contracts through the sale of the entitlements to the electricity sold under those contracts. Unitil Energy and Fitchburg recover in their rates all the costs associated with the divestiture of their power supply portfolios and have secured regulatory approval from the NHPUC and MDPU, respectively, for the recovery of power supply-related stranded costs and other restructuring-related regulatory assets. The companies have a continuing obligation to submit regulatory filings that demonstrate their compliance with regulatory mandates and provide for timely recovery of costs in accordance with their approved restructuring plans.

Note 4: Energy Supply

Natural Gas Supply

Unitil manages gas supply for customers served by Northern Utilities in Maine and New Hampshire as well as customers served by Fitchburg in Massachusetts.

Fitchburg's residential and C&I business customers have the opportunity to purchase their natural gas supply from third-party gas supply vendors. Many large and some medium C&I customers purchase their supplies from third-party suppliers, while most of Fitchburg's residential and small C&I customers continue to purchase their supplies at regulated rates from Fitchburg. Northern Utilities' C&I customers have the opportunity to purchase their natural gas supply from third-party gas supply vendors, and third-party supply is prevalent among Northern Utilities' larger C&I customers. Most small C&I customers, as well as all residential customers, purchase their gas supply from Northern Utilities under regulated rates and tariffs. The approved costs associated with the acquisition of such wholesale natural gas supplies for customers who do not contract with third-party suppliers are recovered on a pass-through basis through periodically-adjusted rates and are included in Purchased Gas in the Consolidated Statements of Earnings.

On November 2, 2011, the Massachusetts Supreme Judicial Court (SJC) issued its decision vacating an order issued on November 2, 2009 by the MDPU in which the MDPU ordered the Company's electric and natural gas distribution utility, Fitchburg, to refund $4.6 million of natural gas costs, plus interest. The MDPU's original order, issued in 2009, found that Fitchburg had engaged in certain price stabilization practices for the 2007 / 2008 and 2008 / 2009 heating seasons without the MDPU's prior approval and that Fitchburg's natural gas purchasing practices were imprudent. The Company appealed the MDPU's decision to the SJC. The SJC's decision vacates the MDPU's order to refund $4.6 million, plus interest, in favor of a $0.2 million refund, plus interest. The Company had previously recorded a pre-tax charge to earnings and recognized a Regulatory Liability of $4.9 million in the fourth quarter of 2009 based on the MDPU's original order. As a result of the decision, the Regulatory Liability has been adjusted and the Company recognized a pre-tax credit of $4.7 million in the fourth quarter of 2011. This credit is recognized on the Company's 2011 Consolidated Statement of Earnings as a $4.5 million reduction in Purchased Gas expense and a reduction of $0.2 million in Interest Expense, net.

Regulated Natural Gas Supply

Fitchburg purchases natural gas under contracts of one year or less, as well as from producers and marketers on the spot market. Fitchburg arranges for gas delivery to its system through its own long-term contracts with Tennessee Gas Pipeline, or in the case of liquefied natural gas (LNG) or liquefied propane gas (LPG), to truck supplies to storage facilities within Fitchburg's service territory.

Fitchburg has available under firm contract 14,057 MMbtu per day for transportation and underground storage capacity to its distribution facilities. As a supplement to pipeline natural gas, Fitchburg owns a propane air gas plant and a LNG storage and vaporization facility. These plants are used principally during peak load periods to augment the supply of pipeline natural gas.

Northern Utilities purchases a majority of its natural gas from U.S. domestic and Canadian suppliers under contracts of one year or less, and on occasion from producers and marketers on the spot market. Northern Utilities arranges for gas delivery to its system through its own long-term contracts with various interstate pipeline and storage facilities, through peaking supply contracts delivered to its system, or in the case of LNG, to truck supplies to storage facilities within Northern Utilities' service territory.

Northern Utilities has available under firm contract 100,000 MMbtu per day of year-round and seasonal transportation capacity to its distribution facilities, and 3.4 Bcf of underground storage. As a supplement to pipeline natural gas, Northern Utilities owns an LNG storage and vaporization facility. This plant is used principally during peak load periods to augment the supply of pipeline natural gas.

Electric Power Supply

The restructuring of the electric utility industry in New Hampshire required the divestiture of Unitil's power supply arrangements and the procurement of replacement supplies, which provided the flexibility for migration of customers to and from utility energy service. Fitchburg, Unitil Energy, and Unitil Power each are members of the New England Power Pool (NEPOOL) and participate in the ISO New England, Inc. (ISO-NE) markets for the purpose of facilitating these wholesale electric power supply transactions, which are necessary to serve Unitil's customers.

As a result of restructuring of the electric utility industry in Massachusetts and New Hampshire, Unitil's customers in both New Hampshire and Massachusetts have the opportunity to purchase their electric supply from competitive third-party energy suppliers. As of December 2011, 106 or 71% of Unitil's largest New Hampshire customers, representing 25% of total New Hampshire electric energy sales, and 28 or 93% of Unitil's largest Massachusetts customers, representing 33% of total Massachusetts electric energy sales, are purchasing their electric power supply in the competitive market.

Regulated Electric Power Supply

In order to provide regulated electric supply service to their customers, Unitil's electric distribution utilities enter into load-following wholesale electric power supply contracts with various wholesale suppliers.

Fitchburg has power supply contracts with various wholesale suppliers for the provision of Basic Service energy supply. MDPU policy dictates the pricing structure and duration of each of these contracts. Currently, all Basic Service power supply contracts for large general accounts are three months in duration and provide 100% of supply requirements. Basic Service power supply contracts for residential, small and medium general service customers are acquired every six months, are 12 months in duration and provide 50% of the supply requirements.

Unitil Energy currently has power supply contracts with various wholesale suppliers for the provision of Default Service to its customers. Unitil Energy procures Default Service supply for its large general service accounts through competitive solicitations for power contracts of three months in duration for 100% of supply requirements. Unitil Energy procures Default Service supply for its other customers through a series of two one-year contracts and two two-year contracts, each providing 25% of the total supply requirements of the group.

The NHPUC and MDPU regularly review alternatives to their procurement policy, which may lead to future changes in this regulated power supply procurement structure.

Regional Electric Transmission and Power Markets

Fitchburg, Unitil Energy and Unitil Power, as well as virtually all New England electric utilities, are participants in the ISO-NE markets. ISO-NE is the Regional Transmission Organization (RTO) in New England. The purpose of ISO-NE is to assure reliable operation of the bulk power system in the most economic manner for the region. Substantially all operation and dispatching of electric generation and bulk transmission capacity in New England is performed on a regional basis. The ISO-NE tariff imposes generating capacity and reserve obligations, and provides for the use of major transmission facilities and support payments associated therewith. The most notable benefits of the ISO-NE are coordinated power system operation in a reliable manner and a supportive business environment for the development of competitive electric markets.

Electric Power Supply Divestiture

In connection with the implementation of retail choice, Unitil Power, which formerly functioned as the wholesale power supply provider for Unitil Energy, and Fitchburg divested their long-term power supply contracts through the sale of the entitlements to the electricity sold under those contracts. Unitil Energy and Fitchburg recover in their rates all the costs associated with the divestiture of their power supply portfolios and have secured regulatory approval from the NHPUC and MDPU, respectively, for the recovery of power supply-related stranded costs and other restructuring-related regulatory assets. The companies have a continuing obligation to submit regulatory filings that demonstrate their compliance with regulatory mandates and provide for timely recovery of costs in accordance with their approved restructuring plans.