Unitil (UTL) 10-Q 25 Oct 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 22, 2018
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Trading Symbol	UTL
Entity Registrant Name	UNITIL CORP
Entity Central Index Key	755,001
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		14,872,955

CONSOLIDATED STATEMENTS OF EARN

CONSOLIDATED STATEMENTS OF EARNINGS - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Revenues
Total Operating Revenues	$ 88.2	$ 84	$ 318.5	$ 290.8
Operating Expenses
Operation and Maintenance	16.4	16.9	51.5	49.4
Depreciation and Amortization	12.4	10.8	37.4	35.2
Taxes Other Than Income Taxes	5.5	4.9	16.5	15.6
Total Operating Expenses	77.9	73.6	269.5	241.1
Operating Income	10.3	10.4	49	49.7
Interest Expense, net	6	5.8	17.9	17.1
Other Expense, net	1.1	0.9	4.1	3.7
Income Before Income Taxes	3.2	3.7	27	28.9
Income Tax Expense	0.4	1.4	5	11.1
Net Income	$ 2.8	$ 2.3	$ 22	$ 17.8
Net Income Per Common Share	$ 0.19	$ 0.16	$ 1.49	$ 1.27
Weighted Average Common Shares Outstanding	14.8	14.1	14.8	14.1
Dividends Declared Per Share of Common Stock	$ 0.365	$ 0.360	$ 1.095	$ 1.080
Gas
Operating Revenues
Total Operating Revenues	$ 25.7	$ 25.1	$ 147.4	$ 131.9
Operating Expenses
Operating Expenses	8.1	8.3	67	56.6
Electric
Operating Revenues
Total Operating Revenues	61.4	57.5	167.6	154.4
Operating Expenses
Operating Expenses	35.5	32.7	97.1	84.3
Other
Operating Revenues
Total Operating Revenues	$ 1.1	$ 1.4	$ 3.5	$ 4.5

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Current Assets:
Cash and Cash Equivalents	$ 6.3	$ 8.9	$ 10.9
Accounts Receivable, net	52.3	67.4	45.8
Accrued Revenue	36	53.3	39.2
Exchange Gas Receivable	10.1	5.8	9.5
Materials and Supplies	7.2	6.9	7.3
Prepayments and Other	8.7	9	9.3
Total Current Assets	120.6	151.3	122
Utility Plant:
Gas	712.7	699.6	646.7
Electric	485.6	476.7	454.6
Common	82.1	67.4	36
Construction Work in Progress	68.4	35.5	113
Total Utility Plant	1,348.8	1,279.2	1,250.3
Less: Accumulated Depreciation	326.5	307.7	303.6
Net Utility Plant	1,022.3	971.5	946.7
Other Noncurrent Assets:
Regulatory Assets	111.6	109.6	102
Other Assets	10	9.5	9.2
Total Other Noncurrent Assets	121.6	119.1	111.2
TOTAL ASSETS	1,264.5	1,241.9	1,179.9
Current Liabilities:
Accounts Payable	27.4	41.5	24.1
Short-Term Debt	69.1	38.3	111.9
Long-Term Debt, Current Portion	31.8	29.8	29.8
Regulatory Liabilities	12.2	9.2	15
Energy Supply Obligations	15	9.7	12.9
Capital Lease Obligations	3.1	3.1	3.1
Other Current Liabilities	21.9	19.4	19.5
Total Current Liabilities	180.5	151	216.3
Noncurrent Liabilities:
Retirement Benefit Obligations	142.4	150.1	155
Deferred Income Taxes, net	86.4	82.9	109.2
Cost of Removal Obligations	91.2	84.3	84.8
Regulatory Liabilities	47.9	48.9
Capital Lease Obligations	3.4	5.7	6.4
Other Noncurrent Liabilities	6.6	5.9	6.3
Total Noncurrent Liabilities	377.9	377.8	361.7
Capitalization:
Long-Term Debt, Less Current Portion	361.1	376.3	303.6
Stockholders' Equity:
Common Equity (Authorized: 25,000,000 and Outstanding: 14,872,011, 14,119,893 and 14,815,585 Shares)	278.3	275.8	243.4
Retained Earnings	66.5	60.8	54.7
Total Common Stock Equity	344.8	336.6	298.1
Preferred Stock	0.2	0.2	0.2
Total Stockholders' Equity	345	336.8	298.3
Total Capitalization	706.1	713.1	601.9
Commitments and Contingencies (Notes 6 & 7)
TOTAL LIABILITIES AND CAPITALIZATION	$ 1,264.5	$ 1,241.9	$ 1,179.9

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Common Stock Authorized	25,000,000	25,000,000	25,000,000
Common Equity Outstanding	14,872,011	14,815,585	14,119,893

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating Activities:
Net Income	$ 22	$ 17.8
Adjustments to Reconcile Net Income to Cash Provided by Operating Activities:
Depreciation and Amortization	37.4	35.2
Deferred Tax Provision	4.6	11.2
Changes in Working Capital Items:
Accounts Receivable	15.1	7.1
Accrued Revenue	17.3	10.3
Exchange Gas Receivable	(4.3)	(1.2)
Regulatory Liabilities	3	4.6
Accounts Payable	(14.1)	(8.3)
Other Changes in Working Capital Items	3.7	(2.6)
Deferred Regulatory and Other Charges	(5.7)	(5.1)
Other, net	(9)	5.7
Cash Provided by Operating Activities	70	74.7
Investing Activities:
Property, Plant and Equipment Additions	(76.3)	(84.2)
Cash (Used in) Investing Activities	(76.3)	(84.2)
Financing Activities:
Proceeds from (Repayment of) Short-Term Debt, net	30.8	30
Repayment of Long-Term Debt	(13.5)	(0.4)
Decrease in Capital Lease Obligations	(2.3)	(1.8)
Net Increase in Exchange Gas Financing	4.1	1.1
Dividends Paid	(16.3)	(15.3)
Proceeds from Issuance of Common Stock, net	0.9	1
Cash Provided by Financing Activities	3.7	14.6
Net (Decrease) Increase in Cash and Cash Equivalents	(2.6)	5.1
Cash and Cash Equivalents at Beginning of Period	8.9	5.8
Cash and Cash Equivalents at End of Period	6.3	10.9
Supplemental Cash Flow Information:
Interest Paid	15.6	15.2
Income Taxes Paid	0.4
Payments on Capital Leases	2.3	2.5
Non-cash Investing Activity:
Capital Expenditures Included in Accounts Payable	$ 1.2	$ 1.8

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN COMMON STOCK EQUITY - USD ($) $ in Millions	Total	Common Equity	Retained Earnings
Beginning Balance at Dec. 31, 2016	$ 292.9	$ 240.7	$ 52.2
Net Income	17.8		17.8
Dividends on Common Shares	(15.3)		(15.3)
Stock Compensation Plans	1.7	1.7
Issuance of Common Shares	1	1
Ending Balance at Sep. 30, 2017	298.1	243.4	54.7
Beginning Balance at Jun. 30, 2017	300.2	242.7	57.5
Net Income	2.3		2.3
Dividends on Common Shares	(5.1)		(5.1)
Stock Compensation Plans	0.4	0.4
Issuance of Common Shares	0.3	0.3
Ending Balance at Sep. 30, 2017	298.1	243.4	54.7
Beginning Balance at Dec. 31, 2017	336.6	275.8	60.8
Net Income	22		22
Dividends on Common Shares	(16.3)		(16.3)
Stock Compensation Plans	1.5	1.5
Issuance of Common Shares	1	1
Ending Balance at Sep. 30, 2018	344.8	278.3	66.5
Beginning Balance at Jun. 30, 2018	347	277.9	69.1
Net Income	2.8		2.8
Dividends on Common Shares	(5.4)		(5.4)
Stock Compensation Plans	0.1	0.1
Issuance of Common Shares	0.3	0.3
Ending Balance at Sep. 30, 2018	$ 344.8	$ 278.3	$ 66.5

CONSOLIDATED STATEMENTS OF CH_2

CONSOLIDATED STATEMENTS OF CHANGES IN COMMON STOCK EQUITY (Parenthetical) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Dividends per Common Share	$ 0.365	$ 0.360	$ 1.095	$ 1.080
Common stock, shares issued	5,423	6,173	19,700	20,564

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2018
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NOTE 1 – SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations non-regulated The Company’s earnings are seasonal and are typically higher in the first and fourth quarters when customers use natural gas for heating purposes. Unitil’s principal business is the local distribution of electricity in the southeastern seacoast and state capital regions of New Hampshire and the greater Fitchburg area of north central Massachusetts, and the local distribution of natural gas in southeastern New Hampshire, portions of southern and central Maine and in the greater Fitchburg area of north central Massachusetts. Unitil has three distribution utility subsidiaries, Unitil Energy, which operates in New Hampshire, Fitchburg, which operates in Massachusetts and Northern Utilities, which operates in New Hampshire and Maine (collectively referred to as the distribution utilities). Granite State is a natural gas transportation pipeline, operating 86 miles of underground gas transmission pipeline primarily located in Maine and New Hampshire. Granite State provides Northern Utilities with interconnection to three major natural gas pipelines and access to domestic natural gas supplies in the south and Canadian natural gas supplies in the north. Granite State derives its revenues principally from the transportation services provided to Northern Utilities and, to a lesser extent, third-party marketers. A fifth utility subsidiary, Unitil Power, formerly functioned as the full requirements wholesale power supply provider for Unitil Energy. In connection with the implementation of electric industry restructuring in New Hampshire, Unitil Power ceased being the wholesale supplier of Unitil Energy on May 1, 2003 and divested of its long-term power supply contracts through the sale of the entitlements to the electricity associated with various electric power supply contracts it had acquired to serve Unitil Energy’s customers. Unitil also has three other wholly-owned subsidiaries: Unitil Service; Unitil Realty; and Unitil Resources. Unitil Service provides, at cost, a variety of administrative and professional services, including regulatory, financial, accounting, human resources, engineering, operations, technology, energy management and management services on a centralized basis to its affiliated Unitil companies. Unitil Realty owns and manages the Company’s corporate office in Hampton, New Hampshire and leases this facility to Unitil Service under a long-term lease arrangement. Unitil Resources is the Company’s wholly-owned non-regulated Basis of Presentation – 10-Q 10-K Utility Revenue Recognition - Billed and unbilled revenue is recorded when service is rendered or energy is delivered to customers. However, the determination of energy sales to individual customers is based on the reading of their meters, which occurs on a systematic basis throughout the month. At the end of each calendar month, amounts of energy delivered to customers since the date of the last meter reading are estimated and the corresponding unbilled revenues are calculated. These unbilled revenues are calculated each month based on estimated customer usage by class and applicable customer rates and are then reversed in the following month when billed to customers. In the first quarter of 2018, the Company adopted Accounting Standards Update (ASU) 2014-09, 2015-14, 2016-08, 2016-10 2017-13, As discussed below, the Company plans to disclose billed and unbilled revenue separately from rate adjustment mechanism revenue in the Notes to the Consolidated Financial Statements for periods in 2018 going forward, and will also provide this disclosure for prior periods for informational purposes. The Company’s billed and unbilled revenue meets the definition of “revenues from contracts with customers” as defined in ASU 2014-09. 980-605-25-3, 2014-09 In the following tables, revenue is classified by the types of goods/services rendered and market/customer type. The lower revenues reported in the three and nine months ended 2018 to account for the reduction in the corporate income tax rate under the Tax Cuts and Jobs Act of 2017 (TCJA) are shown separately in the tables below for informational purposes. Three Months Ended September 30, 2018 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 6.6 $ 33.6 $ 40.2 C&I 11.9 25.3 37.2 Other 1.5 2.6 4.1 Revenue Reductions – TCJA (0.4 ) (0.6 ) (1.0 ) Total Billed and Unbilled Revenue 19.6 60.9 80.5 Rate Adjustment Mechanism Revenue 6.1 0.5 6.6 Total Gas and Electric Operating Revenues $ 25.7 $ 61.4 $ 87.1 Three Months Ended September 30, 2017 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 6.8 $ 29.9 $ 36.7 C&I 11.5 24.3 35.8 Other 1.5 1.3 2.8 Total Billed and Unbilled Revenue 19.8 55.5 75.3 Rate Adjustment Mechanism Revenue 5.3 2.0 7.3 Total Gas and Electric Operating Revenues $ 25.1 $ 57.5 $ 82.6 Nine Months Ended September 30, 2018 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 58.3 $ 95.6 $ 153.9 C&I 84.7 74.1 158.8 Other 11.0 8.6 19.6 Revenue Reductions – TCJA (2.9 ) (2.1 ) (5.0 ) Total Billed and Unbilled Revenue 151.1 176.2 327.3 Rate Adjustment Mechanism Revenue (3.7 ) (8.6 ) (12.3 ) Total Gas and Electric Operating Revenues $ 147.4 $ 167.6 $ 315.0 Nine Months Ended September 30, 2017 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 52.7 $ 80.9 $ 133.6 C&I 73.7 65.0 138.7 Other 9.0 4.3 13.3 Total Billed and Unbilled Revenue 135.4 150.2 285.6 Rate Adjustment Mechanism Revenue (3.5 ) 4.2 0.7 Total Gas and Electric Operating Revenues $ 131.9 $ 154.4 $ 286.3 Fitchburg is subject to revenue decoupling. Revenue decoupling is the term given to the elimination of the dependency of a utility’s distribution revenue on the volume of electricity or natural gas sales. The difference between distribution revenue amounts billed to customers and the targeted revenue decoupling amounts is recorded as an increase or a decrease in Accrued Revenue, which forms the basis for resetting rates for future cash recoveries from, or credits to, customers. These revenue decoupling targets may be adjusted as a result of rate cases that the Company files with the MDPU. The Company estimates that revenue decoupling applies to approximately 27% and 11% of Unitil’s total annual electric and natural gas sales volumes, respectively. Other Operating Revenue – Non-regulated non-regulated As discussed above, the Company adopted ASU 2014-09 2014-09 2014-09, If ASU 2014-09 Three Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Other Operating Revenues ($ millions): 2018 2017 Usource Contract Revenue $ 1.4 $ 1.4 Less: Revenue Sharing Payments 0.3 0.3 Total Other Operating Revenues $ 1.1 $ 1.1 Three Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Operation and Maintenance Expense ($ millions): 2018 2017 Operation and Maintenance Expense $ 16.4 $ 16.6 Nine Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Other Operating Revenues ($ millions): 2018 2017 Usource Contract Revenue $ 4.3 $ 4.5 Less: Revenue Sharing Payments 0.8 0.8 Total Other Operating Revenues $ 3.5 $ 3.7 Nine Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Operation and Maintenance Expense ($ millions): 2018 2017 Operation and Maintenance Expense $ 51.5 $ 48.6 Retirement Benefit Costs – No. 2017-07, Accordingly, for all periods presented in the Consolidated Financial Statements in this Form 10-Q non-service non-service Income Taxes – Provisions for income taxes are calculated in each of the jurisdictions in which the Company operates for each period for which a statement of earnings is presented. The Company accounts for income taxes in accordance with the FASB Codification guidance on Income Taxes, which requires an asset and liability approach for the financial accounting and reporting of income taxes. Significant judgments and estimates are required in determining the current and deferred tax assets and liabilities. The Company’s current and deferred tax assets and liabilities reflect its best assessment of estimated future taxes to be paid. In accordance with the FASB Codification, the Company periodically assesses the realization of its deferred tax assets and liabilities and adjusts the income tax provision, the current tax liability and deferred taxes in the period in which the facts and circumstances which gave rise to the revision become known. Cash and Cash Equivalents – (ISO-NE) ISO-NE. 2-1/2 ISO-NE Allowance for Doubtful Accounts – written-off shut-off. Evaluating The Allowance for Doubtful Accounts as of September 30, 2018, September 30, 2017 and December 31, 2017, which is included in Accounts Receivable, net on the accompanying unaudited consolidated balance sheets, was as follows: ($ millions) September 30, December 31, 2018 2017 2017 Allowance for Doubtful Accounts $ 1.2 $ 1.5 $ 1.6 Accrued Revenue – September 30, December 31, Accrued Revenue ($ millions) 2018 2017 2017 Regulatory Assets – Current $ 26.4 $ 31.3 $ 39.5 Unbilled Revenues 9.6 7.9 13.8 Total Accrued Revenue $ 36.0 $ 39.2 $ 53.3 Exchange Gas Receivable – September 30, December 31, Exchange Gas Receivable ($ millions) 2018 2017 2017 Northern Utilities $ 9.5 $ 8.9 $ 5.4 Fitchburg 0.6 0.6 0.4 Total Exchange Gas Receivable $ 10.1 $ 9.5 $ 5.8 Gas Inventory September 30, December 31, Gas Inventory ($ millions) 2018 2017 2017 Natural Gas $ 0.4 $ 0.4 $ 0.4 Propane 0.4 0.2 0.1 Liquefied Natural Gas & Other 0.1 0.1 0.1 Total Gas Inventory $ 0.9 $ 0.7 $ 0.6 Utility Plant – Regulatory Accounting – September 30, December 31, Regulatory Assets consist of the following ($ millions) 2018 2017 2017 Retirement Benefits $ 88.0 $ 76.2 $ 84.5 Energy Supply & Other Rate Adjustment Mechanisms 24.8 28.2 36.0 Deferred Storm Charges 6.3 6.8 7.2 Environmental 8.9 9.9 9.5 Income Taxes 5.9 6.7 6.5 Other 4.1 5.5 5.4 Total Regulatory Assets 138.0 133.3 149.1 Less: Current Portion of Regulatory Assets (1) 26.4 31.3 39.5 Regulatory Assets – noncurrent $ 111.6 $ 102.0 $ 109.6 (1) Reflects amounts included in Accrued Revenue, discussed above, on the Company’s Consolidated Balance Sheets. September 30, December 31, Regulatory Liabilities consist of the following ($ millions) 2018 2017 2017 Rate Adjustment Mechanisms $ 12.2 $ 11.6 $ 6.9 Gas Pipeline Refund (Note 6) — 3.4 2.3 Income Taxes (Note 8) 47.9 — 48.9 Total Regulatory Liabilities 60.1 15.0 58.1 Less: Current Portion of Regulatory Liabilities 12.2 15.0 9.2 Regulatory Liabilities – noncurrent $ 47.9 $ — $ 48.9 Generally, the Company receives a return on investment on its regulated assets for which a cash outflow has been made. Included in Regulatory Assets as of September 30, 2018 are $6.1 million of environmental costs, rate case costs and other expenditures to be recovered over varying periods in the next seven years. Regulators have authorized recovery of these expenditures, but without a return. Regulatory commissions can reach different conclusions about the recovery of costs, which can have a material impact on the Company’s Consolidated Financial Statements. The Company believes it is probable that its regulated distribution and transmission utilities will recover their investments in long-lived assets, including regulatory assets. If the Company, or a portion of its assets or operations, were to cease meeting the criteria for application of these accounting rules, accounting standards for businesses in general would become applicable and immediate recognition of any previously deferred costs, or a portion of deferred costs, would be required in the year in which the criteria are no longer met, if such deferred costs were not recoverable in the portion of the business that continues to meet the criteria for application of the FASB Codification topic on Regulated Operations. If unable to continue to apply the FASB Codification provisions for Regulated Operations, the Company would be required to apply the provisions for the Discontinuation of Rate-Regulated Accounting included in the FASB Codification. In the Company’s opinion, its regulated operations will be subject to the FASB Codification provisions for Regulated Operations for the foreseeable future. Derivatives – The Company has a regulatory approved hedging program for Northern Utilities designed to fix or cap a portion of its gas supply costs for the coming years of service. Under the program, the Company may purchase call option contracts on NYMEX natural gas futures contracts for future winter period months. Any gains or losses resulting from the change in the fair value of these derivatives are passed through to ratepayers directly through Northern Utilities’ Cost of Gas Clause. The fair value of these derivatives is determined using Level 2 inputs (valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly), specifically based on the NYMEX closing prices for outstanding contracts as of the balance sheet date. As a result of the ratemaking process, the Company records gains and losses resulting from the change in fair value of the derivatives as regulatory liabilities or assets, then reclassifies these gains or losses into Cost of Gas Sales when the gains and losses are passed through to customers through the Cost of Gas Clause. As of September 30, 2018, September 30, 2017 and December 31, 2017 the Company had zero, 1.2 billion and 0.6 billion cubic feet (BCF), respectively, outstanding in natural gas futures and options contracts under its hedging program. As of September 30, 2018, September 30, 2017 and December 31, 2017, the Company’s derivatives that are not designated as hedging instruments under FASB ASC 815-20 Investments in Marketable Securities At September 30, 2018, September 30, 2017 and December 31, 2017, the fair value of the Company’s investments in these trading securities, which are recorded on the Consolidated Balance Sheets in Other Assets, were $5.3 million, $3.4 million and $3.6 million, respectively, as shown in the table below. These investments are valued based on quoted prices from active markets and are categorized in Level 1 as they are actively traded and no valuation adjustments have been applied. Changes in the fair value of these investments are recorded in Other Expense, net. September 30, December 31, Fair Value of Marketable Securities ($ millions) 2018 2017 2017 Equity Funds $ 3.0 $ 1.9 $ 2.1 Fixed Income Funds 2.3 1.5 1.5 Total Marketable Securities $ 5.3 $ 3.4 $ 3.6 Energy Supply Obligations – September 30, December 31, Energy Supply Obligations ($ millions) 2018 2017 2017 Current: Exchange Gas Obligation $ 9.5 $ 8.9 $ 5.4 Renewable Energy Portfolio Standards 5.2 3.7 4.0 Power Supply Contract Divestitures 0.3 0.3 0.3 Total Energy Supply Obligations – Current 15.0 12.9 9.7 Noncurrent: Power Supply Contract Divestitures 0.7 1.0 0.9 Total Energy Supply Obligations $ 15.7 $ 13.9 $ 10.6 Exchange Gas Obligation – Northern Utilities enters into gas exchange agreements under which Northern Utilities releases certain natural gas pipeline and storage assets, resells the natural gas storage inventory to an asset manager and subsequently repurchases the inventory over the course of the natural gas heating season at the same price at which it sold the natural gas inventory to the asset manager. The gas inventory related to these agreements is recorded in Exchange Gas Receivable on the Company’s Consolidated Balance Sheets while the corresponding obligations are recorded in Energy Supply Obligations. Renewable Energy Portfolio Standards – Renewable Energy Portfolio Standards (RPS) require retail electricity suppliers, including public utilities, to demonstrate that required percentages of their sales are met with power generated from certain types of resources or technologies. Compliance is demonstrated by purchasing and retiring Renewable Energy Certificates (REC) generated by facilities approved by the state as qualifying for REC treatment. Unitil Energy and Fitchburg purchase RECs in compliance with RPS legislation in New Hampshire and Massachusetts for supply provided to default service customers. RPS compliance costs are a supply cost that is recovered in customer default service rates. Unitil Energy and Fitchburg collect RPS compliance costs from customers throughout the year and demonstrate compliance for each calendar year on the following July 1. Due to timing differences between collection of revenue from customers and payment of REC costs to suppliers, Unitil Energy and Fitchburg typically maintain accrued revenue for RPS compliance which is recorded in Accrued Revenue with a corresponding liability in Energy Supply Obligations on the Company’s Consolidated Balance Sheets. Fitchburg has entered into long-term renewable contracts for electric energy and/or renewable energy credits pursuant to Massachusetts legislation, specifically, the Act Relative to Green Communities of 2008 and the Act Relative to Competitively Priced Electricity (2012) in the Commonwealth, and the MDPU’s regulations implementing the legislation. The generating facilities associated with three of these contracts have been constructed and are operating. A recent round of long-term renewable energy procurements was conducted during 2016 and several contracts were finalized and submitted to the MDPU in September, 2017 for approval. Additional procurements have been issued in compliance with the Act to Promote Energy Diversity (2016). Fitchburg recovers the costs associated with long-term renewable contracts on a fully reconciling basis through a MDPU-approved cost recovery mechanism. Power Supply Contract Divestitures – As a result of the restructuring of the utility industry in New Hampshire and Massachusetts, Unitil Energy’s and Fitchburg’s customers have the opportunity to purchase their electric or natural gas supplies from third-party suppliers. 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. The obligations related to these divestitures are recorded in Energy Supply Obligations on the Company’s Consolidated Balance Sheets with corresponding regulatory assets recorded in Accrued Revenue (current portion) and Regulatory Assets (long-term portion). Recently Issued Pronouncements – No. 2018-14, 715-20)” In June 2018, the FASB issued ASU No. 2018-07, In March 2017, the FASB issued ASU No. 2017-07, In February 2016, the FASB issued ASU No. 2016-02, . In May 2014, the FASB issued ASU No. 2014-09, The majority of the Company’s revenue, including energy provided to customers, is from tariff offerings that provide natural gas or electricity without a defined contractual term. For such arrangements, the Company generally expects that the revenue from contracts with these customers will continue to be equivalent to the electricity or natural gas supplied and billed in that period (including unbilled revenues) and the adoption of the new guidance will not result in a significant shift in the timing of revenue recognition for such sales. The Company used the modified retrospective method when adopting the new standard on January 1, 2018. The new guidance did not have a material impact to the Consolidated Financial Statements. (See “Utility Revenue Recognition” and “Other Operating Revenue – Non-regulated” In January 2016, the FASB issued Accounting Standards Update (ASU) 2016-01 Other than the pronouncements discussed above, there are no recently issued pronouncements that the Company has not already adopted or that have a material impact on the Company. Subsequent Events –

DIVIDENDS DECLARED PER SHARE

DIVIDENDS DECLARED PER SHARE	9 Months Ended
	Sep. 30, 2018
DIVIDENDS DECLARED PER SHARE	NOTE 2 – DIVIDENDS DECLARED PER SHARE Declaration Date Date Shareholder of Record Date Dividend Amount 10/24/18 11/29/18 11/15/18 $0.365 07/25/18 08/29/18 08/15/18 $0.365 04/25/18 05/29/18 05/15/18 $0.365 01/30/18 02/28/18 02/14/18 $0.365 10/25/17 11/29/17 11/15/17 $0.360 07/26/17 08/29/17 08/15/17 $0.360 04/26/17 05/30/17 05/16/17 $0.360 01/25/17 02/28/17 02/14/17 $0.360

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2018
SEGMENT INFORMATION	NOTE 3 – SEGMENT INFORMATION The following table provides significant segment financial data for the three and nine months ended September 30, 2018 and September 30, 2017 and as of December 31, 2017 (millions): Gas Electric Non- Regulated Other Total Three Months Ended September 30, 2018 Revenues: Billed and Unbilled Revenue $ 19.6 $ 60.9 $ — $ — $ 80.5 Rate Adjustment Mechanism Revenue 6.1 0.5 — — 6.6 Other Operating Revenue – Non-Regulated — — 1.1 — 1.1 Total Operating Revenues $ 25.7 $ 61.4 $ 1.1 $ — $ 88.2 Segment Profit (Loss) (3.2 ) 4.5 0.3 1.2 2.8 Capital Expenditures 30.9 7.2 — 1.0 39.1 Three Months Ended September 30, 2017 Revenues $ 25.1 $ 57.5 $ 1.4 $ — $ 84.0 Segment Profit (Loss) (2.1 ) 4.1 0.3 — 2.3 Capital Expenditures 26.0 10.0 — 3.3 39.3 Nine Months Ended September 30, 2018 Revenues: Billed and Unbilled Revenue $ 151.1 $ 176.2 $ — $ — $ 327.3 Rate Adjustment Mechanism Revenue (3.7 ) (8.6 ) — — (12.3 ) Other Operating Revenue – Non-Regulated — — 3.5 — 3.5 Total Operating Revenues $ 147.4 $ 167.6 $ 3.5 $ — $ 318.5 Segment Profit 9.1 10.2 0.9 1.8 22.0 Capital Expenditures 53.1 20.8 — 2.4 76.3 Segment Assets 730.0 485.7 6.6 42.2 1,264.5 Nine Months Ended September 30, 2017 Revenues $ 131.9 $ 154.4 $ 4.5 $ — $ 290.8 Segment Profit 7.9 9.3 0.8 (0.2 ) 17.8 Capital Expenditures 48.7 23.8 — 11.7 84.2 Segment Assets 661.2 461.2 7.3 50.2 1,179.9 As of December 31, 2017 Segment Assets $ 714.3 $ 476.9 $ 6.7 $ 44.0 $ 1,241.9

DEBT AND FINANCING ARRANGEMENTS

DEBT AND FINANCING ARRANGEMENTS	9 Months Ended
	Sep. 30, 2018
DEBT AND FINANCING ARRANGEMENTS	NOTE 4 – DEBT AND FINANCING ARRANGEMENTS Details on long-term debt at September 30, 2018, September 30, 2017 and December 31, 2017 are shown below: ($ millions) September 30, December 31, 2018 2017 2017 Unitil Corporation: 6.33% Senior Notes, Due May 1, 2022 $ 20.0 $ 20.0 $ 20.0 3.70% Senior Notes, Due August 1, 2026 30.0 30.0 30.0 Unitil Energy First Mortgage Bonds: 5.24% Senior Secured Notes, Due March 2, 2020 10.0 15.0 15.0 8.49% Senior Secured Notes, Due October 14, 2024 7.5 9.0 7.5 6.96% Senior Secured Notes, Due September 1, 2028 20.0 20.0 20.0 8.00% Senior Secured Notes, Due May 1, 2031 15.0 15.0 15.0 6.32% Senior Secured Notes, Due September 15, 2036 15.0 15.0 15.0 Fitchburg: 6.75% Senior Notes, Due November 30, 2023 7.6 9.5 7.6 6.79% Senior Notes, Due October 15, 2025 10.0 10.0 10.0 3.52% Senior Notes, Due November 1, 2027 10.0 — 10.0 7.37% Notes, Due January 15, 2029 12.0 12.0 12.0 5.90% Notes, Due December 15, 2030 15.0 15.0 15.0 7.98% Notes, Due June 1, 2031 14.0 14.0 14.0 4.32% Senior Notes, Due November 1, 2047 15.0 — 15.0 Northern Utilities: 6.95% Senior Notes, Due December 3, 2018 10.0 20.0 10.0 5.29% Senior Notes, Due March 2, 2020 16.6 25.0 25.0 3.52% Senior Notes, Due November 1, 2027 20.0 — 20.0 7.72% Senior Notes, Due December 3, 2038 50.0 50.0 50.0 4.42% Senior Notes, Due October 15, 2044 50.0 50.0 50.0 4.32% Senior Notes, Due November 1, 2047 30.0 — 30.0 Granite State Senior Notes: 7.15% Senior Notes, Due December 15, 2018 3.3 6.7 3.3 3.72% Senior Notes, Due November 1, 2027 15.0 — 15.0 Total Long-Term Debt 396.0 336.2 409.4 Less: Unamortized Debt Issuance Costs 3.1 2.8 3.3 Total Long-Term Debt, net of Unamortized Debt Issuance Costs 392.9 333.4 406.1 Less: Current Portion 31.8 29.8 29.8 Total Long-term Debt, Less Current Portion $ 361.1 $ 303.6 $ 376.3 Fair Value of Long-Term Debt ($ millions) September 30, December 31, 2018 2017 2017 Estimated Fair Value of Long-Term Debt $ 418.7 $ 383.0 $ 457.1 Credit Arrangements On July 25, 2018, the Company entered into a Second Amended and Restated Credit Agreement and related documents (collectively, the “Credit Facility”) with a syndicate of lenders, which amended and restated in its entirety the Company’s prior credit facility. The Credit Facility extends to July 25, 2023, subject to two one-year one-month The Company utilizes the Credit Facility for cash management purposes related to its short-term operating activities. Total gross borrowings were $202.5 million for the nine months ended September 30, 2018. Total gross repayments were $171.7 million for the nine months ended September 30, 2018. The following table details the borrowing limits, amounts outstanding and amounts available under the Credit Facility as of September 30, 2018, September 30, 2017 and December 31, 2017: Credit Facility ($ millions) September 30, December 31, 2018 2017 2017 Limit $ 120.0 $ 120.0 $ 120.0 Short-Term Borrowings Outstanding 69.1 111.9 38.3 Letters of Credit Outstanding — 1.1 — Available $ 50.9 $ 7.0 $ 81.7 The Credit Facility contains customary terms and conditions for credit facilities of this type, including affirmative and negative covenants. There are restrictions on, among other things, the Company’s and its subsidiaries’ ability to permit liens or incur indebtedness, and restrictions on the Company’s ability to merge or consolidate with another entity or change its line of business. The affirmative and negative covenants under the Credit Facility shall apply until the Credit Facility terminates and all amounts borrowed under the Credit Facility are paid in full (or with respect to letters of credit, they are cash collateralized). The only financial covenant in the Credit Facility provides that Funded Debt to Capitalization (as each term is defined in the Credit Facility) cannot exceed 65%, tested on a quarterly basis. At September 30, 2018, September 30, 2017 and December 31, 2017, the Company was in compliance with the covenants contained in the Credit Facility in effect on that date. (See also “Credit Arrangements” in Note 4.) The weighted average interest rates on all short-term borrowings and intercompany money pool transactions were 3.2% and 2.3% for the nine months ended September 30, 2018 and September 30, 2017, respectively. The weighted average interest rate on all short-term borrowings for the twelve months ended December 31, 2017 was 2.4%. On November 1, 2017, Northern Utilities issued $20 million of Notes due 2027 at 3.52% and $30 million of Notes due 2047 at 4.32%. Fitchburg issued $10 million of Notes due 2027 at 3.52% and $15 million of Notes due 2047 at 4.32%. Granite State issued $15 million of Notes due 2027 at 3.72%. Northern Utilities, Fitchburg and Granite State used the net proceeds from these offerings to refinance higher cost long-term debt that matured in 2017, to repay short-term debt and for general corporate purposes. Approximately $0.7 million of costs associated with these issuances have been netted against Long-Term Debt for presentation purposes on the Consolidated Balance Sheets. In April 2014, Unitil Service Corp. entered into a financing arrangement, structured as a capital lease obligation, for various information systems and technology equipment. Final funding under this capital lease occurred on October 30, 2015, resulting in total funding of $13.4 million. The capital lease matures on September 30, 2020. As of September 30, 2018, there are $2.7 million of current and $3.0 million of noncurrent obligations under this capital lease on the Company’s Consolidated Balance Sheets. Unitil Corporation and its utility subsidiaries, Fitchburg, Unitil Energy, Northern Utilities, and Granite State are currently rated “BBB+” by Standard & Poor’s Ratings Services. Unitil Corporation and Granite State are currently rated “Baa2”, and Fitchburg, Unitil Energy and Northern Utilities are currently rated “Baa1” by Moody’s Investors Services. Northern Utilities enters into asset management agreements under which Northern Utilities releases certain natural gas pipeline and storage assets, resells the natural gas storage inventory to an asset manager and subsequently repurchases the inventory over the course of the natural gas heating season at the same price at which it sold the natural gas inventory to the asset manager. There was $9.6 million, $9.0 million and $8.5 million of natural gas storage inventory at September 30, 2018, September 30, 2017 and December 31, 2017, respectively, related to these asset management agreements. The amount of natural gas inventory released in September 2018 and payable in October 2018 is $0.1 million and is recorded in Accounts Payable at September 30, 2018. The amount of natural gas inventory released in September 2017 and payable in October 2017 was $0.1 million and was recorded in Accounts Payable at September 30, 2017. The amount of natural gas inventory released in December 2017 and payable in January 2018 was $3.1 million and was recorded in Accounts Payable at December 31, 2017. Guarantees The Company provides limited guarantees on certain energy and natural gas storage management contracts entered into by the distribution utilities. The Company’s policy is to limit the duration of these guarantees. As of September 30, 2018, there were approximately $5.6 million of guarantees outstanding. The Company also guarantees the payment of principal, interest and other amounts payable on the notes issued by Granite State. As of September 30, 2018, the principal amount outstanding for the 7.15% Granite State notes was $3.3 million.

COMMON STOCK AND PREFERRED STOC

COMMON STOCK AND PREFERRED STOCK	9 Months Ended
	Sep. 30, 2018
COMMON STOCK AND PREFERRED STOCK	NOTE 5 – COMMON STOCK AND PREFERRED STOCK Common Stock The Company’s common stock trades on the New York Stock Exchange under the symbol, “UTL.” The Company had 14,119,893,14,815,585 and 14,872,011 shares of common stock outstanding at September 30, 2017, December 31, 2017 and September 30, 2018, respectively. Unitil Corporation Common Stock Offering Dividend Reinvestment and Stock Purchase Plan - Stock Plan - The maximum number of shares available for awards to participants under the Stock Plan is 677,500. The maximum number of shares that may be awarded in any one calendar year to any one participant is 20,000. In the event of any change in capitalization of the Company, the Compensation Committee is authorized to make an equitable adjustment to the number and kind of shares of common stock that may be delivered under the Stock Plan and, in addition, may authorize and make an equitable adjustment to the Stock Plan’s annual individual award limit. Restricted Shares Outstanding awards of Restricted Shares fully vest over a period of four years at a rate of 25% each year. During the vesting period, dividends on Restricted Shares underlying the award may be credited to a participant’s account. The Company may deduct or withhold, or require a participant to remit to the Company, an amount sufficient to satisfy any taxes required by federal, state, or local law or regulation to be withheld with respect to any taxable event arising in connection with an Award. For purposes of compensation expense, Restricted Shares vest immediately upon a participant becoming eligible for retirement, as defined in the Stock Plan. Prior to the end of the vesting period, the restricted shares are subject to forfeiture if the participant ceases to be employed by the Company other than due to the participant’s death. On January 29, 2018, 37,510 Restricted Shares were issued in conjunction with the Stock Plan with an aggregate market value at the date of issuance of approximately $1.6 million. There were 49,581 and 89,326 non-vested Restricted Stock Units Non-management Restricted Stock Units (Equity Portion) Units Weighted Average Stock Price Restricted Stock Units as of December 31, 2017 52,224 $ 36.22 Restricted Stock Units Granted — — Dividend Equivalents Earned 1,230 $ 46.87 Restricted Stock Units Settled — — Restricted Stock Units as of September 30, 2018 53,454 $ 36.47 There were 44,343 Restricted Stock Units outstanding as of September 30, 2017 with a weighted average stock price of $33.72. On October 1, 2018, there were 11,275 fully-vested Restricted Stock Units issued to members of the Company’s Board of Directors. Included in Other Noncurrent Liabilities on the Company’s Consolidated Balance Sheets as of September 30, 2018, September 30, 2017 and December 31, 2017 is $1.2 million, $0.9 million and $1.0 million, respectively, representing the fair value of liabilities associated with the portion of fully vested RSUs that will be settled in cash. Preferred Stock There was $0.2 million, or 1,893 shares, of Unitil Energy’s 6.00% Series Preferred Stock outstanding as of September 30, 2018, September 30, 2017 and December 31, 2017. There were less than $0.1 million of total dividends declared on Preferred Stock in each of the three and nine month periods ended September 30, 2018 and September 30, 2017, respectively.

REGULATORY MATTERS

REGULATORY MATTERS	9 Months Ended
	Sep. 30, 2018
REGULATORY MATTERS	NOTE 6 – REGULATORY MATTERS UNITIL’S REGULATORY MATTERS ARE DESCRIBED IN NOTE 8 TO THE FINANCIAL STATEMENTS IN ITEM 8 OF PART II OF UNITIL CORPORATION’S FORM 10-K Tax Cuts and Jobs Act of 2017 On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (TCJA) was signed into law. Among other things, the TCJA substantially reduced the corporate income tax rate to 21 percent, effective January 1, 2018. Each state public utility commission, with jurisdiction over the areas that are served by Unitil’s electric and gas subsidiary companies, has issued procedural orders directing how the tax law changes are to be reflected in rates, including requiring that the companies provide certain filings and calculations. Unitil has complied with these orders and has made the required changes to its rates as directed by the commissions. The FERC has also opened a rulemaking proceeding on this matter which has been addressed in a rate settlement filing by Granite State (described below). The Company believes that these matters are substantially resolved and will not have a material impact on its financial position, operating results, or cash flows. In Maine, Northern Utilities’ Maine division recently completed a base rate case (described below). The MPUC’s final order in that docket incorporated the lower tax rates in the calculation of rates for the Company. Similarly, in New Hampshire, Northern Utilities’ New Hampshire division recently completed a base rate case proceeding (described below). The NHPUC’s final order in that docket approved a comprehensive settlement agreement among the Company, the Staff of the Public Utilities Commission and the Office of Consumer Advocate which included the effect of the tax changes in the calculation of the revenue requirement. With respect to Unitil Energy, on April 30, 2018 the NHPUC approved the Company’s annual step increase pursuant to the provisions of its last base rate case, which included adjustments to account for the TCJA’s income tax changes. In Massachusetts, the MDPU issued an order opening an investigation into the effect on rates of the decrease in the federal corporate income tax rate on the MDPU’s regulated utilities, and required each utility subject to its jurisdiction to submit proposals to address the effects of the TCJA and to reduce its rates as of January 1, 2018. The MDPU consolidated an earlier petition filed by the Attorney General requesting such an investigation into its order. On June 29, 2018, the MDPU issued an order accepting Fitchburg’s proposal to decrease the annual revenue requirement of both its gas and electric divisions by $0.8 million each. The MDPU will address the refund of excess accumulated deferred income taxes in phase two of its investigation. An order is pending. On May 2, 2018, Granite State filed an uncontested rate settlement with FERC which accounted for the effects of the TCJA in its rates. The settlement was approved by FERC on June 27, 2018, and complies with and satisfies the FERC Notice of Proposed Rulemaking concerning the justness and reasonableness of rates in light of the corporate income tax reduction under the TCJA. Base Rate Activity Unitil Energy – Base Rates – one-year Fitchburg – Base Rates – Electric – year-to-year Fitchburg – Electric Grid Modernization – pre-authorized Fitchburg – Solar Generation – Fitchburg – Base Rates – Gas – Fitchburg – Gas System Enhancement Program – year-to-year Northern Utilities – Base Rates – Maine – Northern Utilities – Targeted Infrastructure Replacement Adjustment – Maine – Northern Utilities – Targeted Area Build-out Build-out Northern Utilities – Base Rates – New Hampshire – Northern Utilities – Franchise Extensions – New Hampshire – Granite State – Base Rates – Other Matters NHPUC Energy Efficiency Resource Standard Proceeding – Unitil Energy – Electric Grid Modernization – Unitil Energy – Net Metering – time-of-use Unitil Energy – Recent Legislation – non-by-passable Fitchburg – Electric Reconciliation Filing – year-to-year Fitchburg – Service Quality – Fitchburg – Energy Diversity – Fitchburg – Recent Legislation – Fitchburg – Clean Energy RFP – Fitchburg – Other – FERC Transmission Formula Rate Proceedings – ISO-New ISO-New Legal Proceedings The Company is involved in legal and administrative proceedings and claims of various types, which arise in the ordinary course of business. The Company believes, based upon information furnished by counsel and others, that the ultimate resolution of these claims will not have a material impact on its financial position, operating results or cash flows. In early 2009, a putative class action complaint was filed against Unitil’s Massachusetts based utility, Fitchburg, in Massachusetts’ Worcester Superior Court, (captioned Bellermann et al v. Fitchburg Gas and Electric Light Company). The Complaint sought an unspecified amount of damages, including the cost of temporary housing and alternative fuel sources, emotional and physical pain and suffering and property damages allegedly incurred by customers in connection with the loss of electric service during the ice storm in Fitchburg’s service territory in December 2008. The Massachusetts Supreme Judicial Court issued an order denying class certification status in July 2016, though the plaintiffs’ individual claims remain pending. The Company continues to believe these claims are without merit and will continue to defend itself vigorously.

ENVIRONMENTAL MATTERS

ENVIRONMENTAL MATTERS	9 Months Ended
	Sep. 30, 2018
ENVIRONMENTAL MATTERS	NOTE 7 – ENVIRONMENTAL MATTERS UNITIL’S ENVIRONMENTAL MATTERS ARE DESCRIBED IN NOTE 8 TO THE FINANCIAL STATEMENTS IN ITEM 8 OF PART II OF UNITIL CORPORATION’S FORM 10-K The Company’s past and present operations include activities that are generally subject to extensive and complex federal and state environmental laws and regulations. The Company is in material compliance with applicable environmental and safety laws and regulations and, as of September 30, 2018, has not identified any material losses reasonably likely to be incurred in excess of recorded amounts. However, the Company cannot assure that significant costs and liabilities will not be incurred in the future. It is possible that other developments, such as increasingly stringent federal, state or local environmental laws and regulations could result in increased environmental compliance costs. Based on the Company’s current assessment of its environmental responsibilities, existing legal requirements and regulatory policies, the Company does not believe that these environmental costs will have a material adverse effect on the Company’s consolidated financial position or results of operations. Northern Utilities Manufactured Gas Plant Sites – mid-1800s mid-1900s. Northern Utilities has worked with the Maine Department of Environmental Protection and New Hampshire Department of Environmental Services to address environmental concerns with these sites. Northern Utilities or others have substantially completed remediation of all sites, though on site monitoring continues and it is possible that future activities may be required. Supplemental remediation at the Exeter MGP commenced in the second quarter of 2018 and was completed in the third quarter of 2018. The NHPUC and MPUC have approved regulatory mechanisms for the recovery of MGP environmental costs. For Northern Utilities’ New Hampshire division, the NHPUC has approved the recovery of MGP environmental costs over succeeding seven-year periods. For Northern Utilities’ Maine division, the MPUC has authorized the recovery of environmental remediation costs over succeeding five-year periods. The Environmental Obligations table below shows the amounts accrued for Northern Utilities related to estimated future cleanup costs associated with Northern Utilities’ environmental remediation obligations for former MGP sites. Corresponding Regulatory Assets were recorded to reflect that the future recovery of these environmental remediation costs is expected based on regulatory precedent and established practices. Fitchburg’s Manufactured Gas Plant Site – The Environmental Obligations table below shows the amounts accrued for Fitchburg related to estimated future cleanup costs for permanent remediation of the Sawyer Passway site with a corresponding Regulatory Asset recorded to reflect that the recovery of these environmental remediation costs are probable through the regulatory process. The amounts recorded do not assume any amounts are recoverable from insurance companies or other third parties. Fitchburg recovers the environmental response costs incurred at this former MGP site in gas rates pursuant to the terms of a cost recovery agreement approved by the MDPU. Pursuant to this agreement, Fitchburg is authorized to amortize and recover environmental response costs from gas customers over succeeding seven-year periods. The following table sets forth a summary of changes in the Company’s liability for environmental obligations for the nine months ended September 30, 2018 and 2017. The Company’s current and noncurrent environmental obligations are recorded on the Company’s Consolidated Balance Sheets in Other Current Liabilities and Other Noncurrent Liabilities, respectively. Environmental Obligations ($ millions) Fitchburg Northern Total Nine months ended September 30, 2018 2017 2018 2017 2018 2017 Total Balance at Beginning of Period $ 0.1 $ 0.1 $ 2.0 $ 1.8 $ 2.1 $ 1.9 Additions — — 0.6 0.5 0.6 0.5 Less: Payments / Reductions 0.1 — 0.5 0.2 0.6 0.2 Total Balance at End of Period — 0.1 2.1 2.1 2.1 2.2 Less: Current Portion — 0.1 0.6 0.4 0.6 0.5 Noncurrent Balance at End of Period $ — $ — $ 1.5 $ 1.7 $ 1.5 $ 1.7

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2018
INCOME TAXES	NOTE 8: INCOME TAXES The Company filed its tax returns for the year ended December 31, 2017 with the Internal Revenue Service in September 2018 and generated additional federal net operating loss (NOL) carryforward assets principally due to current pension deductions, tax repair deductions, tax depreciation and research and development deductions. As of September 30, 2018, the Company had recorded cumulative federal and state NOL carryforward assets of $18.2 million to offset against taxes payable in future periods. If unused, the Company’s NOL carryforward assets will begin to expire in 2029. In addition, at September 30, 2018, the Company had $3.4 million of cumulative alternative minimum tax credits, general business tax credit and other state tax credit carryforwards to offset future income taxes payable. In March 2018, Unitil Corporation received notice that its Federal Income Tax return filings for the years ended December 31, 2015 and December 31, 2016 are under examination by the IRS. Currently, the Company believes that the ultimate resolution of this examination will not have a material impact on the Company’s financial statements. The Company remains subject to examination by New Hampshire tax authorities for the tax periods ended December 31, 2015; December 31, 2016; and December 31, 2017. Income tax filings for the year ended December 31, 2017 have been filed with the New Hampshire Department of Revenue Administration. The State of Maine has concluded its review of the Company’s tax returns for December 31, 2014, December 31, 2015, and December 31, 2016 which resulted in a small additional refund to the Company. In assessing the near-term use of NOLCs and tax credits, the Company evaluates the expected level of future taxable income, available tax planning strategies, reversals of existing taxable temporary differences and taxable income available in carryback years. Based on all available evidence, both positive and negative, and the weight of that evidence to the extent such evidence can be objectively verified, the Company expects to utilize all of its NOLCs by December 31, 2020 prior to their expiration in 2029. In December 2017, the Tax Cuts and Jobs Act of 2017 (TCJA), which included a reduction to the corporate federal income tax rate to 21% effective January 1, 2018, was signed into law. In accordance with GAAP Accounting Standard 740, the Company revalued its Accumulated Deferred Income Taxes (ADIT) at the new 21% tax rate at which the ADIT will be reversed in future periods. The Company recorded a net Regulatory Liability in the amount of $48.9 million at December 31, 2017 as a result of the ADIT revaluation. On March 15, 2018 FERC issued its Notice of Proposed Rulemaking in Docket No. RM18-11-000 Based on communications received by the Company from its state regulators in rate cases and other regulatory proceedings in the first quarter of 2018 and as prescribed in the TCJA, the recent FERC guidance noted above and IRS normalization rules; the benefit of these excess ADIT amounts will be subject to flow back to customers in future utility rates according to the Average Rate Assumption Method (ARAM). The Company estimates the ARAM flow back period to be between fifteen and twenty years. The Company’s regulators are expected to issue ratemaking guidance in future periods that will determine the final disposition of the re-measurement In addition to the excess $47.1 million ADIT amounts the Company expects to flow through to customers in utility rates, as noted above, there was $1.8 million of excess ADIT at December 31, 2017, related to the implementation of the new federal tax rate of the TCJA, which had not been previously collected from customers through utility rates. The Company will recognize a benefit in its tax provision as the underlying book/tax temporary differences reverse in the current and future periods. The Company evaluated its tax positions at September 30, 2018 in accordance with the FASB Codification, and has concluded that no adjustment for recognition, de-recognition, The Company bills its customers for sales tax in Massachusetts and Maine and consumption tax in New Hampshire. These taxes are remitted to the appropriate departments of revenue in each state and are excluded from revenues on the Company’s unaudited Consolidated Statements of Earnings.

RETIREMENT BENEFIT OBLIGATIONS

RETIREMENT BENEFIT OBLIGATIONS	9 Months Ended
	Sep. 30, 2018
RETIREMENT BENEFIT OBLIGATIONS	NOTE 9: RETIREMENT BENEFIT OBLIGATIONS The Company co-sponsors 10-K The following table includes the key weighted average assumptions used in determining the Company’s benefit plan costs and obligations: 2018 2017 Used to Determine Plan Costs Discount Rate 3.60 % 4.10 % Rate of Compensation Increase 3.00 % 3.00 % Expected Long-term rate of return on plan assets 7.75 % 7.75 % Health Care Cost Trend Rate Assumed for Next Year 7.50 % 8.00 % Ultimate Health Care Cost Trend Rate 4.50 % 4.00 % Year that Ultimate Health Care Cost Trend Rate is reached 2024 2025 The following tables provide the components of the Company’s Retirement plan costs ($000’s): Pension Plan PBOP Plan SERP Three Months Ended September 30, 2018 2017 2018 2017 2018 2017 Service Cost $ 848 $ 824 $ 733 $ 744 $ 122 $ 115 Interest Cost 1,469 1,514 852 978 101 98 Expected Return on Plan Assets (1,946 ) (1,826 ) (409 ) (337 ) — — Prior Service Cost Amortization 81 66 327 350 47 47 Actuarial Loss Amortization 1,447 1,165 346 524 121 74 Sub-total 1,899 1,743 1,849 2,259 391 334 Amounts Capitalized and Deferred (962 ) (932 ) (930 ) (1,226 ) (113 ) (99 ) Net Periodic Benefit Cost Recognized $ 937 $ 811 $ 919 $ 1,033 $ 278 $ 235 Pension Plan PBOP Plan SERP Nine Months Ended September 30, 2018 2017 2018 2017 2018 2017 Service Cost $ 2,544 $ 2,471 $ 2,199 $ 2,231 $ 366 $ 345 Interest Cost 4,407 4,543 2,554 2,935 303 294 Expected Return on Plan Assets (5,838 ) (5,479 ) (1,227 ) (1,010 ) — — Prior Service Cost Amortization 243 197 981 1,049 141 141 Actuarial Loss Amortization 4,341 3,496 1,038 1,573 365 222 Sub-total 5,697 5,228 5,545 6,778 1,175 1,002 Amounts Capitalized and Deferred (2,590 ) (2,402 ) (2,557 ) (3,418 ) (339 ) (297 ) Net Periodic Benefit Cost Recognized $ 3,107 $ 2,826 $ 2,988 $ 3,360 $ 836 $ 705 Employer Contributions As of September 30, 2018, the Company had made $16.6 million and $3.0 million of contributions to its Pension and PBOP Plans, respectively, in 2018. The Company, along with its subsidiaries, expects to continue to make contributions to its Pension and PBOP Plans in 2018 and future years at minimum required and discretionary funding levels consistent with the amounts recovered in the distribution utilities’ rates for these Pension and PBOP Plan costs. As of September 30, 2018, the Company had made $87,500 of benefit payments under the SERP in 2018. The Company presently anticipates making an additional $313,100 of benefit payments under the SERP in 2018.

SUMMARY OF SIGNIFICANT ACCOUN_2

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2018
Nature of Operations	Nature of Operations non-regulated The Company’s earnings are seasonal and are typically higher in the first and fourth quarters when customers use natural gas for heating purposes. Unitil’s principal business is the local distribution of electricity in the southeastern seacoast and state capital regions of New Hampshire and the greater Fitchburg area of north central Massachusetts, and the local distribution of natural gas in southeastern New Hampshire, portions of southern and central Maine and in the greater Fitchburg area of north central Massachusetts. Unitil has three distribution utility subsidiaries, Unitil Energy, which operates in New Hampshire, Fitchburg, which operates in Massachusetts and Northern Utilities, which operates in New Hampshire and Maine (collectively referred to as the distribution utilities). Granite State is a natural gas transportation pipeline, operating 86 miles of underground gas transmission pipeline primarily located in Maine and New Hampshire. Granite State provides Northern Utilities with interconnection to three major natural gas pipelines and access to domestic natural gas supplies in the south and Canadian natural gas supplies in the north. Granite State derives its revenues principally from the transportation services provided to Northern Utilities and, to a lesser extent, third-party marketers. A fifth utility subsidiary, Unitil Power, formerly functioned as the full requirements wholesale power supply provider for Unitil Energy. In connection with the implementation of electric industry restructuring in New Hampshire, Unitil Power ceased being the wholesale supplier of Unitil Energy on May 1, 2003 and divested of its long-term power supply contracts through the sale of the entitlements to the electricity associated with various electric power supply contracts it had acquired to serve Unitil Energy’s customers. Unitil also has three other wholly-owned subsidiaries: Unitil Service; Unitil Realty; and Unitil Resources. Unitil Service provides, at cost, a variety of administrative and professional services, including regulatory, financial, accounting, human resources, engineering, operations, technology, energy management and management services on a centralized basis to its affiliated Unitil companies. Unitil Realty owns and manages the Company’s corporate office in Hampton, New Hampshire and leases this facility to Unitil Service under a long-term lease arrangement. Unitil Resources is the Company’s wholly-owned non-regulated
Basis of Presentation	Basis of Presentation – 10-Q 10-K
Utility Revenue Recognition	Utility Revenue Recognition - Billed and unbilled revenue is recorded when service is rendered or energy is delivered to customers. However, the determination of energy sales to individual customers is based on the reading of their meters, which occurs on a systematic basis throughout the month. At the end of each calendar month, amounts of energy delivered to customers since the date of the last meter reading are estimated and the corresponding unbilled revenues are calculated. These unbilled revenues are calculated each month based on estimated customer usage by class and applicable customer rates and are then reversed in the following month when billed to customers. In the first quarter of 2018, the Company adopted Accounting Standards Update (ASU) 2014-09, 2015-14, 2016-08, 2016-10 2017-13, As discussed below, the Company plans to disclose billed and unbilled revenue separately from rate adjustment mechanism revenue in the Notes to the Consolidated Financial Statements for periods in 2018 going forward, and will also provide this disclosure for prior periods for informational purposes. The Company’s billed and unbilled revenue meets the definition of “revenues from contracts with customers” as defined in ASU 2014-09. 980-605-25-3, 2014-09 In the following tables, revenue is classified by the types of goods/services rendered and market/customer type. The lower revenues reported in the three and nine months ended 2018 to account for the reduction in the corporate income tax rate under the Tax Cuts and Jobs Act of 2017 (TCJA) are shown separately in the tables below for informational purposes. Three Months Ended September 30, 2018 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 6.6 $ 33.6 $ 40.2 C&I 11.9 25.3 37.2 Other 1.5 2.6 4.1 Revenue Reductions – TCJA (0.4 ) (0.6 ) (1.0 ) Total Billed and Unbilled Revenue 19.6 60.9 80.5 Rate Adjustment Mechanism Revenue 6.1 0.5 6.6 Total Gas and Electric Operating Revenues $ 25.7 $ 61.4 $ 87.1 Three Months Ended September 30, 2017 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 6.8 $ 29.9 $ 36.7 C&I 11.5 24.3 35.8 Other 1.5 1.3 2.8 Total Billed and Unbilled Revenue 19.8 55.5 75.3 Rate Adjustment Mechanism Revenue 5.3 2.0 7.3 Total Gas and Electric Operating Revenues $ 25.1 $ 57.5 $ 82.6 Nine Months Ended September 30, 2018 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 58.3 $ 95.6 $ 153.9 C&I 84.7 74.1 158.8 Other 11.0 8.6 19.6 Revenue Reductions – TCJA (2.9 ) (2.1 ) (5.0 ) Total Billed and Unbilled Revenue 151.1 176.2 327.3 Rate Adjustment Mechanism Revenue (3.7 ) (8.6 ) (12.3 ) Total Gas and Electric Operating Revenues $ 147.4 $ 167.6 $ 315.0 Nine Months Ended September 30, 2017 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 52.7 $ 80.9 $ 133.6 C&I 73.7 65.0 138.7 Other 9.0 4.3 13.3 Total Billed and Unbilled Revenue 135.4 150.2 285.6 Rate Adjustment Mechanism Revenue (3.5 ) 4.2 0.7 Total Gas and Electric Operating Revenues $ 131.9 $ 154.4 $ 286.3 Fitchburg is subject to revenue decoupling. Revenue decoupling is the term given to the elimination of the dependency of a utility’s distribution revenue on the volume of electricity or natural gas sales. The difference between distribution revenue amounts billed to customers and the targeted revenue decoupling amounts is recorded as an increase or a decrease in Accrued Revenue, which forms the basis for resetting rates for future cash recoveries from, or credits to, customers. These revenue decoupling targets may be adjusted as a result of rate cases that the Company files with the MDPU. The Company estimates that revenue decoupling applies to approximately 27% and 11% of Unitil’s total annual electric and natural gas sales volumes, respectively.
Other Operating Revenue - Non-regulated	Other Operating Revenue – Non-regulated non-regulated As discussed above, the Company adopted ASU 2014-09 2014-09 2014-09, If ASU 2014-09 Three Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Other Operating Revenues ($ millions): 2018 2017 Usource Contract Revenue $ 1.4 $ 1.4 Less: Revenue Sharing Payments 0.3 0.3 Total Other Operating Revenues $ 1.1 $ 1.1 Three Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Operation and Maintenance Expense ($ millions): 2018 2017 Operation and Maintenance Expense $ 16.4 $ 16.6 Nine Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Other Operating Revenues ($ millions): 2018 2017 Usource Contract Revenue $ 4.3 $ 4.5 Less: Revenue Sharing Payments 0.8 0.8 Total Other Operating Revenues $ 3.5 $ 3.7 Nine Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Operation and Maintenance Expense ($ millions): 2018 2017 Operation and Maintenance Expense $ 51.5 $ 48.6
Retirement Benefit Costs	Retirement Benefit Costs – No. 2017-07, Accordingly, for all periods presented in the Consolidated Financial Statements in this Form 10-Q non-service non-service
Income Taxes	Income Taxes – Provisions for income taxes are calculated in each of the jurisdictions in which the Company operates for each period for which a statement of earnings is presented. The Company accounts for income taxes in accordance with the FASB Codification guidance on Income Taxes, which requires an asset and liability approach for the financial accounting and reporting of income taxes. Significant judgments and estimates are required in determining the current and deferred tax assets and liabilities. The Company’s current and deferred tax assets and liabilities reflect its best assessment of estimated future taxes to be paid. In accordance with the FASB Codification, the Company periodically assesses the realization of its deferred tax assets and liabilities and adjusts the income tax provision, the current tax liability and deferred taxes in the period in which the facts and circumstances which gave rise to the revision become known.
Cash and Cash Equivalents	Cash and Cash Equivalents – (ISO-NE) ISO-NE. 2-1/2 ISO-NE
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts – written-off shut-off. Evaluating The Allowance for Doubtful Accounts as of September 30, 2018, September 30, 2017 and December 31, 2017, which is included in Accounts Receivable, net on the accompanying unaudited consolidated balance sheets, was as follows: ($ millions) September 30, December 31, 2018 2017 2017 Allowance for Doubtful Accounts $ 1.2 $ 1.5 $ 1.6
Accrued Revenue	Accrued Revenue – September 30, December 31, Accrued Revenue ($ millions) 2018 2017 2017 Regulatory Assets – Current $ 26.4 $ 31.3 $ 39.5 Unbilled Revenues 9.6 7.9 13.8 Total Accrued Revenue $ 36.0 $ 39.2 $ 53.3
Exchange Gas Receivable	Exchange Gas Receivable – September 30, December 31, Exchange Gas Receivable ($ millions) 2018 2017 2017 Northern Utilities $ 9.5 $ 8.9 $ 5.4 Fitchburg 0.6 0.6 0.4 Total Exchange Gas Receivable $ 10.1 $ 9.5 $ 5.8
Gas Inventory	Gas Inventory September 30, December 31, Gas Inventory ($ millions) 2018 2017 2017 Natural Gas $ 0.4 $ 0.4 $ 0.4 Propane 0.4 0.2 0.1 Liquefied Natural Gas & Other 0.1 0.1 0.1 Total Gas Inventory $ 0.9 $ 0.7 $ 0.6
Utility Plant	Utility Plant –
Regulatory Accounting	Regulatory Accounting – September 30, December 31, Regulatory Assets consist of the following ($ millions) 2018 2017 2017 Retirement Benefits $ 88.0 $ 76.2 $ 84.5 Energy Supply & Other Rate Adjustment Mechanisms 24.8 28.2 36.0 Deferred Storm Charges 6.3 6.8 7.2 Environmental 8.9 9.9 9.5 Income Taxes 5.9 6.7 6.5 Other 4.1 5.5 5.4 Total Regulatory Assets 138.0 133.3 149.1 Less: Current Portion of Regulatory Assets (1) 26.4 31.3 39.5 Regulatory Assets – noncurrent $ 111.6 $ 102.0 $ 109.6 (1) Reflects amounts included in Accrued Revenue, discussed above, on the Company’s Consolidated Balance Sheets. September 30, December 31, Regulatory Liabilities consist of the following ($ millions) 2018 2017 2017 Rate Adjustment Mechanisms $ 12.2 $ 11.6 $ 6.9 Gas Pipeline Refund (Note 6) — 3.4 2.3 Income Taxes (Note 8) 47.9 — 48.9 Total Regulatory Liabilities 60.1 15.0 58.1 Less: Current Portion of Regulatory Liabilities 12.2 15.0 9.2 Regulatory Liabilities – noncurrent $ 47.9 $ — $ 48.9 Generally, the Company receives a return on investment on its regulated assets for which a cash outflow has been made. Included in Regulatory Assets as of September 30, 2018 are $6.1 million of environmental costs, rate case costs and other expenditures to be recovered over varying periods in the next seven years. Regulators have authorized recovery of these expenditures, but without a return. Regulatory commissions can reach different conclusions about the recovery of costs, which can have a material impact on the Company’s Consolidated Financial Statements. The Company believes it is probable that its regulated distribution and transmission utilities will recover their investments in long-lived assets, including regulatory assets. If the Company, or a portion of its assets or operations, were to cease meeting the criteria for application of these accounting rules, accounting standards for businesses in general would become applicable and immediate recognition of any previously deferred costs, or a portion of deferred costs, would be required in the year in which the criteria are no longer met, if such deferred costs were not recoverable in the portion of the business that continues to meet the criteria for application of the FASB Codification topic on Regulated Operations. If unable to continue to apply the FASB Codification provisions for Regulated Operations, the Company would be required to apply the provisions for the Discontinuation of Rate-Regulated Accounting included in the FASB Codification. In the Company’s opinion, its regulated operations will be subject to the FASB Codification provisions for Regulated Operations for the foreseeable future.
Derivatives	Derivatives – The Company has a regulatory approved hedging program for Northern Utilities designed to fix or cap a portion of its gas supply costs for the coming years of service. Under the program, the Company may purchase call option contracts on NYMEX natural gas futures contracts for future winter period months. Any gains or losses resulting from the change in the fair value of these derivatives are passed through to ratepayers directly through Northern Utilities’ Cost of Gas Clause. The fair value of these derivatives is determined using Level 2 inputs (valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly), specifically based on the NYMEX closing prices for outstanding contracts as of the balance sheet date. As a result of the ratemaking process, the Company records gains and losses resulting from the change in fair value of the derivatives as regulatory liabilities or assets, then reclassifies these gains or losses into Cost of Gas Sales when the gains and losses are passed through to customers through the Cost of Gas Clause. As of September 30, 2018, September 30, 2017 and December 31, 2017 the Company had zero, 1.2 billion and 0.6 billion cubic feet (BCF), respectively, outstanding in natural gas futures and options contracts under its hedging program. As of September 30, 2018, September 30, 2017 and December 31, 2017, the Company’s derivatives that are not designated as hedging instruments under FASB ASC 815-20
Investments in Marketable Securities	Investments in Marketable Securities At September 30, 2018, September 30, 2017 and December 31, 2017, the fair value of the Company’s investments in these trading securities, which are recorded on the Consolidated Balance Sheets in Other Assets, were $5.3 million, $3.4 million and $3.6 million, respectively, as shown in the table below. These investments are valued based on quoted prices from active markets and are categorized in Level 1 as they are actively traded and no valuation adjustments have been applied. Changes in the fair value of these investments are recorded in Other Expense, net. September 30, December 31, Fair Value of Marketable Securities ($ millions) 2018 2017 2017 Equity Funds $ 3.0 $ 1.9 $ 2.1 Fixed Income Funds 2.3 1.5 1.5 Total Marketable Securities $ 5.3 $ 3.4 $ 3.6
Energy Supply Obligations	Energy Supply Obligations – September 30, December 31, Energy Supply Obligations ($ millions) 2018 2017 2017 Current: Exchange Gas Obligation $ 9.5 $ 8.9 $ 5.4 Renewable Energy Portfolio Standards 5.2 3.7 4.0 Power Supply Contract Divestitures 0.3 0.3 0.3 Total Energy Supply Obligations – Current 15.0 12.9 9.7 Noncurrent: Power Supply Contract Divestitures 0.7 1.0 0.9 Total Energy Supply Obligations $ 15.7 $ 13.9 $ 10.6 Exchange Gas Obligation – Northern Utilities enters into gas exchange agreements under which Northern Utilities releases certain natural gas pipeline and storage assets, resells the natural gas storage inventory to an asset manager and subsequently repurchases the inventory over the course of the natural gas heating season at the same price at which it sold the natural gas inventory to the asset manager. The gas inventory related to these agreements is recorded in Exchange Gas Receivable on the Company’s Consolidated Balance Sheets while the corresponding obligations are recorded in Energy Supply Obligations. Renewable Energy Portfolio Standards – Renewable Energy Portfolio Standards (RPS) require retail electricity suppliers, including public utilities, to demonstrate that required percentages of their sales are met with power generated from certain types of resources or technologies. Compliance is demonstrated by purchasing and retiring Renewable Energy Certificates (REC) generated by facilities approved by the state as qualifying for REC treatment. Unitil Energy and Fitchburg purchase RECs in compliance with RPS legislation in New Hampshire and Massachusetts for supply provided to default service customers. RPS compliance costs are a supply cost that is recovered in customer default service rates. Unitil Energy and Fitchburg collect RPS compliance costs from customers throughout the year and demonstrate compliance for each calendar year on the following July 1. Due to timing differences between collection of revenue from customers and payment of REC costs to suppliers, Unitil Energy and Fitchburg typically maintain accrued revenue for RPS compliance which is recorded in Accrued Revenue with a corresponding liability in Energy Supply Obligations on the Company’s Consolidated Balance Sheets. Fitchburg has entered into long-term renewable contracts for electric energy and/or renewable energy credits pursuant to Massachusetts legislation, specifically, the Act Relative to Green Communities of 2008 and the Act Relative to Competitively Priced Electricity (2012) in the Commonwealth, and the MDPU’s regulations implementing the legislation. The generating facilities associated with three of these contracts have been constructed and are operating. A recent round of long-term renewable energy procurements was conducted during 2016 and several contracts were finalized and submitted to the MDPU in September, 2017 for approval. Additional procurements have been issued in compliance with the Act to Promote Energy Diversity (2016). Fitchburg recovers the costs associated with long-term renewable contracts on a fully reconciling basis through a MDPU-approved cost recovery mechanism. Power Supply Contract Divestitures – As a result of the restructuring of the utility industry in New Hampshire and Massachusetts, Unitil Energy’s and Fitchburg’s customers have the opportunity to purchase their electric or natural gas supplies from third-party suppliers. 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. The obligations related to these divestitures are recorded in Energy Supply Obligations on the Company’s Consolidated Balance Sheets with corresponding regulatory assets recorded in Accrued Revenue (current portion) and Regulatory Assets (long-term portion).
Recently Issued Pronouncements	Recently Issued Pronouncements – No. 2018-14, 715-20)” In June 2018, the FASB issued ASU No. 2018-07, In March 2017, the FASB issued ASU No. 2017-07, In February 2016, the FASB issued ASU No. 2016-02, . In May 2014, the FASB issued ASU No. 2014-09, The majority of the Company’s revenue, including energy provided to customers, is from tariff offerings that provide natural gas or electricity without a defined contractual term. For such arrangements, the Company generally expects that the revenue from contracts with these customers will continue to be equivalent to the electricity or natural gas supplied and billed in that period (including unbilled revenues) and the adoption of the new guidance will not result in a significant shift in the timing of revenue recognition for such sales. The Company used the modified retrospective method when adopting the new standard on January 1, 2018. The new guidance did not have a material impact to the Consolidated Financial Statements. (See “Utility Revenue Recognition” and “Other Operating Revenue – Non-regulated” In January 2016, the FASB issued Accounting Standards Update (ASU) 2016-01 Other than the pronouncements discussed above, there are no recently issued pronouncements that the Company has not already adopted or that have a material impact on the Company.
Subsequent Events	Subsequent Events –

SUMMARY OF SIGNIFICANT ACCOUN_3

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2018
Components of Gas and Electric Operating Revenue	In the following tables, revenue is classified by the types of goods/services rendered and market/customer type. The lower revenues reported in the three and nine months ended 2018 to account for the reduction in the corporate income tax rate under the Tax Cuts and Jobs Act of 2017 (TCJA) are shown separately in the tables below for informational purposes. Three Months Ended September 30, 2018 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 6.6 $ 33.6 $ 40.2 C&I 11.9 25.3 37.2 Other 1.5 2.6 4.1 Revenue Reductions – TCJA (0.4 ) (0.6 ) (1.0 ) Total Billed and Unbilled Revenue 19.6 60.9 80.5 Rate Adjustment Mechanism Revenue 6.1 0.5 6.6 Total Gas and Electric Operating Revenues $ 25.7 $ 61.4 $ 87.1 Three Months Ended September 30, 2017 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 6.8 $ 29.9 $ 36.7 C&I 11.5 24.3 35.8 Other 1.5 1.3 2.8 Total Billed and Unbilled Revenue 19.8 55.5 75.3 Rate Adjustment Mechanism Revenue 5.3 2.0 7.3 Total Gas and Electric Operating Revenues $ 25.1 $ 57.5 $ 82.6 Nine Months Ended September 30, 2018 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 58.3 $ 95.6 $ 153.9 C&I 84.7 74.1 158.8 Other 11.0 8.6 19.6 Revenue Reductions – TCJA (2.9 ) (2.1 ) (5.0 ) Total Billed and Unbilled Revenue 151.1 176.2 327.3 Rate Adjustment Mechanism Revenue (3.7 ) (8.6 ) (12.3 ) Total Gas and Electric Operating Revenues $ 147.4 $ 167.6 $ 315.0 Nine Months Ended September 30, 2017 Gas and Electric Operating Revenues ($ millions): Gas Electric Total Billed and Unbilled Revenue: Residential $ 52.7 $ 80.9 $ 133.6 C&I 73.7 65.0 138.7 Other 9.0 4.3 13.3 Total Billed and Unbilled Revenue 135.4 150.2 285.6 Rate Adjustment Mechanism Revenue (3.5 ) 4.2 0.7 Total Gas and Electric Operating Revenues $ 131.9 $ 154.4 $ 286.3
Schedule of Other Operating Revenues and Operating Expenses	If ASU 2014-09 Three Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Other Operating Revenues ($ millions): 2018 2017 Usource Contract Revenue $ 1.4 $ 1.4 Less: Revenue Sharing Payments 0.3 0.3 Total Other Operating Revenues $ 1.1 $ 1.1 Three Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Operation and Maintenance Expense ($ millions): 2018 2017 Operation and Maintenance Expense $ 16.4 $ 16.6 Nine Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Other Operating Revenues ($ millions): 2018 2017 Usource Contract Revenue $ 4.3 $ 4.5 Less: Revenue Sharing Payments 0.8 0.8 Total Other Operating Revenues $ 3.5 $ 3.7 Nine Months Ended September 30, As Reported If ASU 2014-09 Had Been in Effect Operation and Maintenance Expense ($ millions): 2018 2017 Operation and Maintenance Expense $ 51.5 $ 48.6
Allowance for Doubtful Accounts Included in Accounts Receivable Net	The Allowance for Doubtful Accounts as of September 30, 2018, September 30, 2017 and December 31, 2017, which is included in Accounts Receivable, net on the accompanying unaudited consolidated balance sheets, was as follows: ($ millions) September 30, December 31, 2018 2017 2017 Allowance for Doubtful Accounts $ 1.2 $ 1.5 $ 1.6
Components of Accrued Revenue	The following table shows the components of Accrued Revenue as of September 30, 2018, September 30, 2018 and December 31, 2017. September 30, December 31, Accrued Revenue ($ millions) 2018 2017 2017 Regulatory Assets – Current $ 26.4 $ 31.3 $ 39.5 Unbilled Revenues 9.6 7.9 13.8 Total Accrued Revenue $ 36.0 $ 39.2 $ 53.3
Components of Exchange Gas Receivable	The following table shows the components of Exchange Gas Receivable as of September 30, 2018, September 30, 2017 and December 31, 2017. September 30, December 31, Exchange Gas Receivable ($ millions) 2018 2017 2017 Northern Utilities $ 9.5 $ 8.9 $ 5.4 Fitchburg 0.6 0.6 0.4 Total Exchange Gas Receivable $ 10.1 $ 9.5 $ 5.8
Components of Gas Inventory	The following table shows the components of gas inventory as of September 30, 2018, September 30, 2017 and December 31, 2017 which are recorded on the Consolidated Balance Sheets in Prepayments and Other. September 30, December 31, Gas Inventory ($ millions) 2018 2017 2017 Natural Gas $ 0.4 $ 0.4 $ 0.4 Propane 0.4 0.2 0.1 Liquefied Natural Gas & Other 0.1 0.1 0.1 Total Gas Inventory $ 0.9 $ 0.7 $ 0.6
Regulatory Assets	September 30, December 31, Regulatory Assets consist of the following ($ millions) 2018 2017 2017 Retirement Benefits $ 88.0 $ 76.2 $ 84.5 Energy Supply & Other Rate Adjustment Mechanisms 24.8 28.2 36.0 Deferred Storm Charges 6.3 6.8 7.2 Environmental 8.9 9.9 9.5 Income Taxes 5.9 6.7 6.5 Other 4.1 5.5 5.4 Total Regulatory Assets 138.0 133.3 149.1 Less: Current Portion of Regulatory Assets (1) 26.4 31.3 39.5 Regulatory Assets – noncurrent $ 111.6 $ 102.0 $ 109.6 (1) Reflects amounts included in Accrued Revenue, discussed above, on the Company’s Consolidated Balance Sheets.
Regulatory Liabilities	September 30, December 31, Regulatory Liabilities consist of the following ($ millions) 2018 2017 2017 Rate Adjustment Mechanisms $ 12.2 $ 11.6 $ 6.9 Gas Pipeline Refund (Note 6) — 3.4 2.3 Income Taxes (Note 8) 47.9 — 48.9 Total Regulatory Liabilities 60.1 15.0 58.1 Less: Current Portion of Regulatory Liabilities 12.2 15.0 9.2 Regulatory Liabilities – noncurrent $ 47.9 $ — $ 48.9
Fair Value of Marketable Securities	Changes in the fair value of these investments are recorded in Other Expense, net. September 30, December 31, Fair Value of Marketable Securities ($ millions) 2018 2017 2017 Equity Funds $ 3.0 $ 1.9 $ 2.1 Fixed Income Funds 2.3 1.5 1.5 Total Marketable Securities $ 5.3 $ 3.4 $ 3.6
Components of Energy Supply Obligations	The following discussion and table summarize the nature and amounts of the items recorded as current and noncurrent Energy Supply Obligations on the Company’s Consolidated Balance Sheets. The noncurrent portion of Energy Supply Obligations is recorded in Other Noncurrent Liabilities on the Company’s Consolidated Balance Sheets. September 30, December 31, Energy Supply Obligations ($ millions) 2018 2017 2017 Current: Exchange Gas Obligation $ 9.5 $ 8.9 $ 5.4 Renewable Energy Portfolio Standards 5.2 3.7 4.0 Power Supply Contract Divestitures 0.3 0.3 0.3 Total Energy Supply Obligations – Current 15.0 12.9 9.7 Noncurrent: Power Supply Contract Divestitures 0.7 1.0 0.9 Total Energy Supply Obligations $ 15.7 $ 13.9 $ 10.6

DIVIDENDS DECLARED PER SHARE (T

DIVIDENDS DECLARED PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2018
Schedule of Dividends Declared	Declaration Date Date Shareholder of Record Date Dividend Amount 10/24/18 11/29/18 11/15/18 $0.365 07/25/18 08/29/18 08/15/18 $0.365 04/25/18 05/29/18 05/15/18 $0.365 01/30/18 02/28/18 02/14/18 $0.365 10/25/17 11/29/17 11/15/17 $0.360 07/26/17 08/29/17 08/15/17 $0.360 04/26/17 05/30/17 05/16/17 $0.360 01/25/17 02/28/17 02/14/17 $0.360

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2018
Significant Segment Financial Data	The following table provides significant segment financial data for the three and nine months ended September 30, 2018 and September 30, 2017 and as of December 31, 2017 (millions): Gas Electric Non- Regulated Other Total Three Months Ended September 30, 2018 Revenues: Billed and Unbilled Revenue $ 19.6 $ 60.9 $ — $ — $ 80.5 Rate Adjustment Mechanism Revenue 6.1 0.5 — — 6.6 Other Operating Revenue – Non-Regulated — — 1.1 — 1.1 Total Operating Revenues $ 25.7 $ 61.4 $ 1.1 $ — $ 88.2 Segment Profit (Loss) (3.2 ) 4.5 0.3 1.2 2.8 Capital Expenditures 30.9 7.2 — 1.0 39.1 Three Months Ended September 30, 2017 Revenues $ 25.1 $ 57.5 $ 1.4 $ — $ 84.0 Segment Profit (Loss) (2.1 ) 4.1 0.3 — 2.3 Capital Expenditures 26.0 10.0 — 3.3 39.3 Nine Months Ended September 30, 2018 Revenues: Billed and Unbilled Revenue $ 151.1 $ 176.2 $ — $ — $ 327.3 Rate Adjustment Mechanism Revenue (3.7 ) (8.6 ) — — (12.3 ) Other Operating Revenue – Non-Regulated — — 3.5 — 3.5 Total Operating Revenues $ 147.4 $ 167.6 $ 3.5 $ — $ 318.5 Segment Profit 9.1 10.2 0.9 1.8 22.0 Capital Expenditures 53.1 20.8 — 2.4 76.3 Segment Assets 730.0 485.7 6.6 42.2 1,264.5 Nine Months Ended September 30, 2017 Revenues $ 131.9 $ 154.4 $ 4.5 $ — $ 290.8 Segment Profit 7.9 9.3 0.8 (0.2 ) 17.8 Capital Expenditures 48.7 23.8 — 11.7 84.2 Segment Assets 661.2 461.2 7.3 50.2 1,179.9 As of December 31, 2017 Segment Assets $ 714.3 $ 476.9 $ 6.7 $ 44.0 $ 1,241.9

DEBT AND FINANCING ARRANGEMEN_2

DEBT AND FINANCING ARRANGEMENTS (Tables)	9 Months Ended
	Sep. 30, 2018
Details on Long Term Debt	Details on long-term debt at September 30, 2018, September 30, 2017 and December 31, 2017 are shown below: ($ millions) September 30, December 31, 2018 2017 2017 Unitil Corporation: 6.33% Senior Notes, Due May 1, 2022 $ 20.0 $ 20.0 $ 20.0 3.70% Senior Notes, Due August 1, 2026 30.0 30.0 30.0 Unitil Energy First Mortgage Bonds: 5.24% Senior Secured Notes, Due March 2, 2020 10.0 15.0 15.0 8.49% Senior Secured Notes, Due October 14, 2024 7.5 9.0 7.5 6.96% Senior Secured Notes, Due September 1, 2028 20.0 20.0 20.0 8.00% Senior Secured Notes, Due May 1, 2031 15.0 15.0 15.0 6.32% Senior Secured Notes, Due September 15, 2036 15.0 15.0 15.0 Fitchburg: 6.75% Senior Notes, Due November 30, 2023 7.6 9.5 7.6 6.79% Senior Notes, Due October 15, 2025 10.0 10.0 10.0 3.52% Senior Notes, Due November 1, 2027 10.0 — 10.0 7.37% Notes, Due January 15, 2029 12.0 12.0 12.0 5.90% Notes, Due December 15, 2030 15.0 15.0 15.0 7.98% Notes, Due June 1, 2031 14.0 14.0 14.0 4.32% Senior Notes, Due November 1, 2047 15.0 — 15.0 Northern Utilities: 6.95% Senior Notes, Due December 3, 2018 10.0 20.0 10.0 5.29% Senior Notes, Due March 2, 2020 16.6 25.0 25.0 3.52% Senior Notes, Due November 1, 2027 20.0 — 20.0 7.72% Senior Notes, Due December 3, 2038 50.0 50.0 50.0 4.42% Senior Notes, Due October 15, 2044 50.0 50.0 50.0 4.32% Senior Notes, Due November 1, 2047 30.0 — 30.0 Granite State Senior Notes: 7.15% Senior Notes, Due December 15, 2018 3.3 6.7 3.3 3.72% Senior Notes, Due November 1, 2027 15.0 — 15.0 Total Long-Term Debt 396.0 336.2 409.4 Less: Unamortized Debt Issuance Costs 3.1 2.8 3.3 Total Long-Term Debt, net of Unamortized Debt Issuance Costs 392.9 333.4 406.1 Less: Current Portion 31.8 29.8 29.8 Total Long-term Debt, Less Current Portion $ 361.1 $ 303.6 $ 376.3
Fair Value of Long Term Debt	($ millions) September 30, December 31, 2018 2017 2017 Estimated Fair Value of Long-Term Debt $ 418.7 $ 383.0 $ 457.1
Borrowing Limits Amounts Outstanding and Amounts Available under Credit Facility	The following table details the borrowing limits, amounts outstanding and amounts available under the Credit Facility as of September 30, 2018, September 30, 2017 and December 31, 2017: Credit Facility ($ millions) September 30, December 31, 2018 2017 2017 Limit $ 120.0 $ 120.0 $ 120.0 Short-Term Borrowings Outstanding 69.1 111.9 38.3 Letters of Credit Outstanding — 1.1 — Available $ 50.9 $ 7.0 $ 81.7

COMMON STOCK AND PREFERRED ST_2

COMMON STOCK AND PREFERRED STOCK (Tables)	9 Months Ended
	Sep. 30, 2018
Restricted Stock Units Issued	The equity portion of Restricted Stock Units activity during the nine months ended September 30, 2018 in conjunction with the Stock Plan are presented in the following table: Restricted Stock Units (Equity Portion) Units Weighted Average Stock Price Restricted Stock Units as of December 31, 2017 52,224 $ 36.22 Restricted Stock Units Granted — — Dividend Equivalents Earned 1,230 $ 46.87 Restricted Stock Units Settled — — Restricted Stock Units as of September 30, 2018 53,454 $ 36.47

ENVIRONMENTAL MATTERS (Tables)

ENVIRONMENTAL MATTERS (Tables)	9 Months Ended
	Sep. 30, 2018
Environmental Obligations Recognized by Company	The following table sets forth a summary of changes in the Company’s liability for environmental obligations for the nine months ended September 30, 2018 and 2017. The Company’s current and noncurrent environmental obligations are recorded on the Company’s Consolidated Balance Sheets in Other Current Liabilities and Other Noncurrent Liabilities, respectively. Environmental Obligations ($ millions) Fitchburg Northern Total Nine months ended September 30, 2018 2017 2018 2017 2018 2017 Total Balance at Beginning of Period $ 0.1 $ 0.1 $ 2.0 $ 1.8 $ 2.1 $ 1.9 Additions — — 0.6 0.5 0.6 0.5 Less: Payments / Reductions 0.1 — 0.5 0.2 0.6 0.2 Total Balance at End of Period — 0.1 2.1 2.1 2.1 2.2 Less: Current Portion — 0.1 0.6 0.4 0.6 0.5 Noncurrent Balance at End of Period $ — $ — $ 1.5 $ 1.7 $ 1.5 $ 1.7

RETIREMENT BENEFIT OBLIGATIONS

RETIREMENT BENEFIT OBLIGATIONS (Tables)	9 Months Ended
	Sep. 30, 2018
Key Weighted Average Assumptions Used in Determining Benefit Plan Costs and Obligations	The following table includes the key weighted average assumptions used in determining the Company’s benefit plan costs and obligations: 2018 2017 Used to Determine Plan Costs Discount Rate 3.60 % 4.10 % Rate of Compensation Increase 3.00 % 3.00 % Expected Long-term rate of return on plan assets 7.75 % 7.75 % Health Care Cost Trend Rate Assumed for Next Year 7.50 % 8.00 % Ultimate Health Care Cost Trend Rate 4.50 % 4.00 % Year that Ultimate Health Care Cost Trend Rate is reached 2024 2025
Components of Retirement Plan Costs	The following tables provide the components of the Company’s Retirement plan costs ($000’s): Pension Plan PBOP Plan SERP Three Months Ended September 30, 2018 2017 2018 2017 2018 2017 Service Cost $ 848 $ 824 $ 733 $ 744 $ 122 $ 115 Interest Cost 1,469 1,514 852 978 101 98 Expected Return on Plan Assets (1,946 ) (1,826 ) (409 ) (337 ) — — Prior Service Cost Amortization 81 66 327 350 47 47 Actuarial Loss Amortization 1,447 1,165 346 524 121 74 Sub-total 1,899 1,743 1,849 2,259 391 334 Amounts Capitalized and Deferred (962 ) (932 ) (930 ) (1,226 ) (113 ) (99 ) Net Periodic Benefit Cost Recognized $ 937 $ 811 $ 919 $ 1,033 $ 278 $ 235 Pension Plan PBOP Plan SERP Nine Months Ended September 30, 2018 2017 2018 2017 2018 2017 Service Cost $ 2,544 $ 2,471 $ 2,199 $ 2,231 $ 366 $ 345 Interest Cost 4,407 4,543 2,554 2,935 303 294 Expected Return on Plan Assets (5,838 ) (5,479 ) (1,227 ) (1,010 ) — — Prior Service Cost Amortization 243 197 981 1,049 141 141 Actuarial Loss Amortization 4,341 3,496 1,038 1,573 365 222 Sub-total 5,697 5,228 5,545 6,778 1,175 1,002 Amounts Capitalized and Deferred (2,590 ) (2,402 ) (2,557 ) (3,418 ) (339 ) (297 ) Net Periodic Benefit Cost Recognized $ 3,107 $ 2,826 $ 2,988 $ 3,360 $ 836 $ 705

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) Bcf in Billions	3 Months Ended		9 Months Ended
	Sep. 30, 2018USD ($)Bcf	Sep. 30, 2017USD ($)Bcf	Sep. 30, 2018USD ($)SubsidiarymiBcf	Sep. 30, 2017USD ($)Bcf	Dec. 31, 2017USD ($)Bcf
Significant Accounting Policies [Line Items]
Length Of Pipeline | mi			86
Revenue sharing payments	$ 300,000	$ 300,000	$ 800,000	$ 800,000
Other	87,100,000	82,600,000	315,000,000	286,300,000
Operation and Maintenance Expense	16,400,000	16,900,000	51,500,000	49,400,000
Cost of removal obligation	91,200,000	84,800,000	91,200,000	84,800,000	$ 84,300,000
Regulatory Assets	$ 138,000,000	$ 133,300,000	$ 138,000,000	$ 133,300,000	$ 149,100,000
Number of Natural Gas Storage Outstanding | Bcf	0	1.2	0	1.2	0.6
Investments in trading securities	$ 5,300,000	$ 3,400,000	$ 5,300,000	$ 3,400,000	$ 3,600,000
ASU 2014-09
Significant Accounting Policies [Line Items]
Revenue sharing payments		300,000		800,000
Operation and Maintenance Expense		16,600,000		48,600,000
Non Service
Significant Accounting Policies [Line Items]
Non-service cost net periodic benefit costs	1,200,000	900,000	4,100,000	3,600,000
Not Designated as Hedging Instruments
Significant Accounting Policies [Line Items]
Derivative Assets, not designated as hedging instruments	$ 0	100,000	$ 0	100,000	100,000
Annual Electric Sales Volume
Significant Accounting Policies [Line Items]
Percentage of total sales volumes revenue subject to RDM			27.00%
Annual Natural Gas Sales Volume
Significant Accounting Policies [Line Items]
Percentage of total sales volumes revenue subject to RDM			11.00%
Maximum
Significant Accounting Policies [Line Items]
Cash equivalents maturity period	3 months
ISO-NE Obligations
Significant Accounting Policies [Line Items]
Cash Deposits	$ 3,200,000	4,800,000	$ 3,200,000	4,800,000	2,900,000
Natural Gas Hedging Program
Significant Accounting Policies [Line Items]
Cash Deposits	0	0	0	0	$ 0
Environmental and Rate Case Costs and Other Expenditures | Recovered over the next seven years
Significant Accounting Policies [Line Items]
Regulatory Assets	$ 6,100,000		$ 6,100,000
Restatement Adjustment [Member] | ASU 2014-09
Significant Accounting Policies [Line Items]
Other		(300,000)		(800,000)
Operation and Maintenance Expense		$ (300,000)		$ (800,000)
Utilities
Significant Accounting Policies [Line Items]
Number of Subsidiaries | Subsidiary			3
Unitil Service; Unitil Realty; and Unitil Resources
Significant Accounting Policies [Line Items]
Number of Subsidiaries | Subsidiary			3

Components of Gas and Electric

Components of Gas and Electric Operating Revenue (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	$ 87.1	$ 82.6	$ 315	$ 286.3
Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	80.5	75.3	327.3	285.6
Rate Adjustment Mechanism Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	6.6	7.3	(12.3)	0.7
Gas Segment
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	25.7	25.1	147.4	131.9
Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	19.6	19.8	151.1	135.4
Gas Segment | Rate Adjustment Mechanism Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	6.1	5.3	(3.7)	(3.5)
Electric
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	61.4	57.5	167.6	154.4
Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	60.9	55.5	176.2	150.2
Electric | Rate Adjustment Mechanism Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	0.5	2	(8.6)	4.2
Residential | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	40.2	36.7	153.9	133.6
Residential | Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	6.6	6.8	58.3	52.7
Residential | Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	33.6	29.9	95.6	80.9
C&I | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	37.2	35.8	158.8	138.7
C&I | Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	11.9	11.5	84.7	73.7
C&I | Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	25.3	24.3	74.1	65
Other | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	4.1	2.8	19.6	13.3
Other | Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	1.5	1.5	11	9
Other | Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	2.6	$ 1.3	8.6	$ 4.3
Revenue Reduction - TCJA | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	(1)		(5)
Revenue Reduction - TCJA | Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	(0.4)		(2.9)
Revenue Reduction - TCJA | Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	$ (0.6)		$ (2.1)

Schedule of Other Operating Rev

Schedule of Other Operating Revenues and Operating Expenses (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Component of Operating Other Cost and Expense [Abstract]
Revenue	$ 87.1	$ 82.6	$ 315	$ 286.3
Less: Revenue Sharing Payments	0.3	0.3	0.8	0.8
Total Other Operating Revenues	1.1		3.5
Operation and Maintenance Expense	16.4	16.9	51.5	49.4
Usource Contract Revenues [Member]
Component of Operating Other Cost and Expense [Abstract]
Revenue	$ 1.4		$ 4.3
ASU 2014-09
Component of Operating Other Cost and Expense [Abstract]
Less: Revenue Sharing Payments		0.3		0.8
Total Other Operating Revenues		1.1		3.7
Operation and Maintenance Expense		16.6		48.6
ASU 2014-09 | Usource Contract Revenues [Member]
Component of Operating Other Cost and Expense [Abstract]
Revenue		$ 1.4		$ 4.5

Allowance for Doubtful Accounts

Allowance for Doubtful Accounts Included in Accounts Receivable Net (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Valuation Allowance [Line Items]
Allowance for Doubtful Accounts	$ 1.2	$ 1.6	$ 1.5

Components of Accrued Revenue (

Components of Accrued Revenue (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Deferred Revenue Arrangement [Line Items]
Accrued Revenue	$ 36	$ 53.3	$ 39.2
Unbilled Revenues
Deferred Revenue Arrangement [Line Items]
Accrued Revenue	9.6	13.8	7.9
Regulatory Assets
Deferred Revenue Arrangement [Line Items]
Accrued Revenue	$ 26.4	$ 39.5	$ 31.3

Components of Exchange Gas Rece

Components of Exchange Gas Receivable (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Receivables [Line Items]
Total Exchange Gas Receivable	$ 10.1	$ 5.8	$ 9.5
Northern Utilities Inc
Receivables [Line Items]
Total Exchange Gas Receivable	9.5	5.4	8.9
Fitchburg Gas and Electric Light Company
Receivables [Line Items]
Total Exchange Gas Receivable	$ 0.6	$ 0.4	$ 0.6

Components of Gas Inventory (De

Components of Gas Inventory (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 0.9	$ 0.6	$ 0.7
Liquefied Natural Gas & Other
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	0.1	0.1	0.1
Natural Gas
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	0.4	0.4	0.4
Propane
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 0.4	$ 0.1	$ 0.2

Regulatory Assets (Detail)

Regulatory Assets (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Regulatory Assets [Line Items]
Regulatory Assets		$ 138	$ 149.1	$ 133.3
Less: Current Portion of Regulatory Assets	[1]	26.4	39.5	31.3
Regulatory Assets - noncurrent		111.6	109.6	102
Environmental Matters
Regulatory Assets [Line Items]
Regulatory Assets		8.9	9.5	9.9
Other Assets
Regulatory Assets [Line Items]
Regulatory Assets		4.1	5.4	5.5
Retirement Benefits
Regulatory Assets [Line Items]
Regulatory Assets		88	84.5	76.2
Deferred Storm Charges
Regulatory Assets [Line Items]
Regulatory Assets		6.3	7.2	6.8
Income Taxes
Regulatory Assets [Line Items]
Regulatory Assets		5.9	6.5	6.7
Energy Supply & Other Rate Adjustment Mechanisms
Regulatory Assets [Line Items]
Regulatory Assets		$ 24.8	$ 36	$ 28.2
[1]	Reflects amounts included in Accrued Revenue, discussed above, on the Company's Consolidated Balance Sheets.

Regulatory Liabilities (Detail)

Regulatory Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 60.1	$ 58.1	$ 15
Less: Current Portion of Regulatory Liabilities	12.2	9.2	15
Regulatory Liabilities-noncurrent	47.9	48.9
Rate Adjustment Mechanisms
Regulatory Liabilities [Line Items]
Regulatory Liabilities	12.2	6.9	11.6
Gas Pipeline Refund
Regulatory Liabilities [Line Items]
Regulatory Liabilities		2.3	$ 3.4
Income Tax Related Liabilities
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 47.9	$ 48.9

Fair Value of Marketable Securi

Fair Value of Marketable Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	$ 5.3	$ 3.6	$ 3.4
Fair Value, Inputs, Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	5.3	3.6	3.4
Fair Value, Inputs, Level 1 | Equity Funds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	3	2.1	1.9
Fair Value, Inputs, Level 1 | Fixed Income Funds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	$ 2.3	$ 1.5	$ 1.5

Components of Energy Supply Obl

Components of Energy Supply Obligations (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Contractual Obligation [Line Items]
Energy Supply Obligations-Current	$ 15	$ 9.7	$ 12.9
Power Supply Contract Divestitures, Noncurrent	0.7	0.9	1
Total Energy Supply Obligations	15.7	10.6	13.9
Exchange Gas Obligation
Contractual Obligation [Line Items]
Energy Supply Obligations-Current	9.5	5.4	8.9
Renewable Energy Portfolio Standards
Contractual Obligation [Line Items]
Energy Supply Obligations-Current	5.2	4	3.7
Power Supply Contract Divestitures
Contractual Obligation [Line Items]
Energy Supply Obligations-Current	$ 0.3	$ 0.3	$ 0.3

Dividends Declared Per Share (D

Dividends Declared Per Share (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Dividends Payable [Line Items]
Dividend Amount	$ 0.365	$ 0.360	$ 1.095	$ 1.080
Group One
Dividends Payable [Line Items]
Declaration Date			Oct. 24, 2018
Date Paid (Payable)			Nov. 29, 2018
Shareholder of Record Date			Nov. 15, 2018
Dividend Amount			$ 0.365
Group Two
Dividends Payable [Line Items]
Declaration Date			Jul. 25, 2018
Date Paid (Payable)			Aug. 29, 2018
Shareholder of Record Date			Aug. 15, 2018
Dividend Amount			$ 0.365
Group Three
Dividends Payable [Line Items]
Declaration Date			Apr. 25, 2018
Date Paid (Payable)			May 29, 2018
Shareholder of Record Date			May 15, 2018
Dividend Amount			$ 0.365
Group Four
Dividends Payable [Line Items]
Declaration Date			Jan. 30, 2018
Date Paid (Payable)			Feb. 28, 2018
Shareholder of Record Date			Feb. 14, 2018
Dividend Amount			$ 0.365
Group Five
Dividends Payable [Line Items]
Declaration Date			Oct. 25, 2017
Date Paid (Payable)			Nov. 29, 2017
Shareholder of Record Date			Nov. 15, 2017
Dividend Amount			$ 0.360
Group Six
Dividends Payable [Line Items]
Declaration Date			Jul. 26, 2017
Date Paid (Payable)			Aug. 29, 2017
Shareholder of Record Date			Aug. 15, 2017
Dividend Amount			$ 0.360
Group Seven
Dividends Payable [Line Items]
Declaration Date			Apr. 26, 2017
Date Paid (Payable)			May 30, 2017
Shareholder of Record Date			May 16, 2017
Dividend Amount			$ 0.360
Group Eight
Dividends Payable [Line Items]
Declaration Date			Jan. 25, 2017
Date Paid (Payable)			Feb. 28, 2017
Shareholder of Record Date			Feb. 14, 2017
Dividend Amount			$ 0.360

Significant Segment Financial D

Significant Segment Financial Data (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other Operating Revenue - Non-Regulated	$ 1.1		$ 3.5
Revenues	88.2	$ 84	318.5	$ 290.8
Segment Profit (Loss)	2.8	2.3	22	17.8
Capital Expenditures	39.1	39.3	76.3	84.2
Segment Assets	1,264.5	1,179.9	1,264.5	1,179.9	$ 1,241.9
Billed and Unbilled Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	80.5		327.3
Rate Adjustment Mechanism Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	6.6		(12.3)
Gas Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	25.7	25.1	147.4	131.9
Segment Profit (Loss)	(3.2)	(2.1)	9.1	7.9
Capital Expenditures	30.9	26	53.1	48.7
Segment Assets	730	661.2	730	661.2	714.3
Gas Segment | Billed and Unbilled Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	19.6		151.1
Gas Segment | Rate Adjustment Mechanism Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	6.1		(3.7)
Electric
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	61.4	57.5	167.6	154.4
Segment Profit (Loss)	4.5	4.1	10.2	9.3
Capital Expenditures	7.2	10	20.8	23.8
Segment Assets	485.7	461.2	485.7	461.2	476.9
Electric | Billed and Unbilled Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	60.9		176.2
Electric | Rate Adjustment Mechanism Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	0.5		(8.6)
All Other Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment Profit (Loss)	1.2		1.8	(0.2)
Capital Expenditures	1	3.3	2.4	11.7
Segment Assets	42.2	50.2	42.2	50.2	44
Unregulated Operation
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other Operating Revenue - Non-Regulated	1.1		3.5
Revenues	1.1	1.4	3.5	4.5
Segment Profit (Loss)	0.3	0.3	0.9	0.8
Segment Assets	$ 6.6	$ 7.3	$ 6.6	$ 7.3	$ 6.7

Details on Long Term Debt (Deta

Details on Long Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Total Long-Term Debt	$ 396	$ 409.4	$ 336.2
Less: Unamortized Debt Issuance Costs	3.1	3.3	2.8
Long-Term Debt	392.9	406.1	333.4
Less: Current Portion	31.8	29.8	29.8
Total Long-term Debt, Less Current Portion	361.1	376.3	303.6
Long-Term Debt	392.9	406.1	333.4
6.33% Senior Notes, Due May 1, 2022
Debt Instrument [Line Items]
Total Long-Term Debt	20	20	20
3.70% Senior Notes, Due August 1, 2026
Debt Instrument [Line Items]
Total Long-Term Debt	30	30	30
Unitil Energy Systems Inc | First Mortgage Bonds 5.24% Senior Secured Notes, Due March 2, 2020
Debt Instrument [Line Items]
Total Long-Term Debt	10	15	15
Unitil Energy Systems Inc | First Mortgage Bonds 8.49% Senior Secured Notes, Due October 14, 2024
Debt Instrument [Line Items]
Total Long-Term Debt	7.5	7.5	9
Unitil Energy Systems Inc | First Mortgage Bonds 6.96% Senior Secured Notes, Due September 1, 2028
Debt Instrument [Line Items]
Total Long-Term Debt	20	20	20
Unitil Energy Systems Inc | First Mortgage Bonds 8.00% Senior Secured Notes, Due May 1, 2031
Debt Instrument [Line Items]
Total Long-Term Debt	15	15	15
Unitil Energy Systems Inc | First Mortgage Bonds 6.32% Senior Secured Notes, Due September 15, 2036
Debt Instrument [Line Items]
Total Long-Term Debt	15	15	15
Fitchburg Gas and Electric Light Company | 6.75% Senior Notes, Due November 30, 2023
Debt Instrument [Line Items]
Total Long-Term Debt	7.6	7.6	9.5
Fitchburg Gas and Electric Light Company | 6.79% Senior Notes, Due October 15, 2025
Debt Instrument [Line Items]
Total Long-Term Debt	10	10	10
Fitchburg Gas and Electric Light Company | 3.52% Senior Notes, Due November 1, 2027
Debt Instrument [Line Items]
Total Long-Term Debt	10	10
Fitchburg Gas and Electric Light Company | 7.37% Notes, Due January 15, 2029
Debt Instrument [Line Items]
Total Long-Term Debt	12	12	12
Fitchburg Gas and Electric Light Company | 5.90% Notes, Due December 15, 2030
Debt Instrument [Line Items]
Total Long-Term Debt	15	15	15
Fitchburg Gas and Electric Light Company | 7.98% Notes, Due June 1, 2031
Debt Instrument [Line Items]
Total Long-Term Debt	14	14	14
Fitchburg Gas and Electric Light Company | 4.32% Senior Notes, Due November 1, 2047
Debt Instrument [Line Items]
Total Long-Term Debt	15	15
Northern Utilities Inc | 3.52% Senior Notes, Due November 1, 2027
Debt Instrument [Line Items]
Total Long-Term Debt	20	20
Northern Utilities Inc | 4.32% Senior Notes, Due November 1, 2047
Debt Instrument [Line Items]
Total Long-Term Debt	30	30
Northern Utilities Inc | 6.95% Senior Notes, Due December 3, 2018
Debt Instrument [Line Items]
Total Long-Term Debt	10	10	20
Northern Utilities Inc | 5.29% Senior Notes, Due March 2, 2020
Debt Instrument [Line Items]
Total Long-Term Debt	16.6	25	25
Northern Utilities Inc | 7.72% Senior Notes, Due December 3, 2038
Debt Instrument [Line Items]
Total Long-Term Debt	50	50	50
Northern Utilities Inc | 4.42% Senior Notes, Due October 15, 2044
Debt Instrument [Line Items]
Total Long-Term Debt	50	50	50
Granite State Gas Transmission Inc | 7.15% Senior Notes, Due December 15, 2018
Debt Instrument [Line Items]
Total Long-Term Debt	3.3	3.3	$ 6.7
Granite State Gas Transmission Inc | 3.72% Senior Notes, Due November 1, 2027
Debt Instrument [Line Items]
Total Long-Term Debt	$ 15	$ 15

Details on Long Term Debt (Pare

Details on Long Term Debt (Parenthetical) (Detail)	Nov. 01, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
6.33% Senior Notes, Due May 1, 2022
Debt Instrument [Line Items]
Stated interest rate		6.33%	6.33%	6.33%
Debt instrument due date		May 1, 2022	May 1, 2022	May 1, 2022
3.70% Senior Notes, Due August 1, 2026
Debt Instrument [Line Items]
Stated interest rate		3.70%	3.70%	3.70%
Debt instrument due date		Aug. 1, 2026	Aug. 1, 2026	Aug. 1, 2026
First Mortgage Bonds 5.24% Senior Secured Notes, Due March 2, 2020 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate		5.24%	5.24%	5.24%
Debt instrument due date		Mar. 2, 2020	Mar. 2, 2020	Mar. 2, 2020
First Mortgage Bonds 8.49% Senior Secured Notes, Due October 14, 2024 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate		8.49%	8.49%	8.49%
Debt instrument due date		Oct. 14, 2024	Oct. 14, 2024	Oct. 14, 2024
First Mortgage Bonds 6.96% Senior Secured Notes, Due September 1, 2028 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate		6.96%	6.96%	6.96%
Debt instrument due date		Sep. 1, 2028	Sep. 1, 2028	Sep. 1, 2028
First Mortgage Bonds 8.00% Senior Secured Notes, Due May 1, 2031 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate		8.00%	8.00%	8.00%
Debt instrument due date		May 1, 2031	May 1, 2031	May 1, 2031
First Mortgage Bonds 6.32% Senior Secured Notes, Due September 15, 2036 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate		6.32%	6.32%	6.32%
Debt instrument due date		Sep. 15, 2036	Sep. 15, 2036	Sep. 15, 2036
6.75% Senior Notes, Due November 30, 2023 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate		6.75%	6.75%	6.75%
Debt instrument due date		Nov. 30, 2023	Nov. 30, 2023	Nov. 30, 2023
6.79% Senior Notes, Due October 15, 2025 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate		6.79%	6.79%	6.79%
Debt instrument due date		Oct. 15, 2025	Oct. 15, 2025	Oct. 15, 2025
3.52% Senior Notes, Due November 1, 2027 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate	3.52%	3.52%	3.52%	3.52%
Debt instrument due date	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027
3.52% Senior Notes, Due November 1, 2027 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate	3.52%	3.52%	3.52%	3.52%
Debt instrument due date	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027
7.37% Notes, Due January 15, 2029 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate		7.37%	7.37%	7.37%
Debt instrument due date		Jan. 15, 2029	Jan. 15, 2029	Jan. 15, 2029
5.90% Notes, Due December 15, 2030 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate		5.90%	5.90%	5.90%
Debt instrument due date		Dec. 15, 2030	Dec. 15, 2030	Dec. 15, 2030
7.98% Notes, Due June 1, 2031 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate		7.98%	7.98%	7.98%
Debt instrument due date		Jun. 1, 2031	Jun. 1, 2031	Jun. 1, 2031
4.32% Senior Notes, Due November 1, 2047 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate	4.32%	4.32%	4.32%	4.32%
Debt instrument due date	Nov. 1, 2047	Nov. 1, 2047	Nov. 1, 2047	Nov. 1, 2047
4.32% Senior Notes, Due November 1, 2047 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate	4.32%	4.32%	4.32%	4.32%
Debt instrument due date	Nov. 1, 2047	Nov. 1, 2047	Nov. 1, 2047	Nov. 1, 2047
6.95% Senior Notes, Due December 3, 2018 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate		6.95%	6.95%	6.95%
Debt instrument due date		Dec. 3, 2018	Dec. 3, 2018	Dec. 3, 2018
5.29% Senior Notes, Due March 2, 2020 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate		5.29%	5.29%	5.29%
Debt instrument due date		Mar. 2, 2020	Mar. 2, 2020	Mar. 2, 2020
7.72% Senior Notes, Due December 3, 2038 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate		7.72%	7.72%	7.72%
Debt instrument due date		Dec. 3, 2038	Dec. 3, 2038	Dec. 3, 2038
4.42% Senior Notes, Due October 15, 2044 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate		4.42%	4.42%	4.42%
Debt instrument due date		Oct. 15, 2044	Oct. 15, 2044	Oct. 15, 2044
7.15% Senior Notes, Due December 15, 2018 | Granite State Gas Transmission Inc
Debt Instrument [Line Items]
Stated interest rate		7.15%	7.15%	7.15%
Debt instrument due date		Dec. 15, 2018	Dec. 15, 2018	Dec. 15, 2018
3.72% Senior Notes, Due November 1, 2027 | Granite State Gas Transmission Inc
Debt Instrument [Line Items]
Stated interest rate	3.72%	3.72%	3.72%	3.72%
Debt instrument due date	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027

Estimated Fair Value of Long Te

Estimated Fair Value of Long Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Fair Value, Inputs, Level 2
Debt Instrument [Line Items]
Estimated Fair Value of Long-Term Debt	$ 418.7	$ 457.1	$ 383

Debt and Financing Arrangemen_3

Debt and Financing Arrangements - Additional Information (Detail) - USD ($)	Jul. 25, 2018	Nov. 01, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Oct. 30, 2015
Line of Credit Facility [Line Items]
Weighted average interest rate on short term borrowings			3.20%	2.30%	2.40%
Issuance of long-term debt		$ 700,000
Capital lease obligation, current			$ 3,100,000	$ 3,100,000	$ 3,100,000
Capital lease obligation, noncurrent			3,400,000	6,400,000	5,700,000
Accounts Payable			27,400,000	24,100,000	41,500,000
Guarantee outstanding			$ 5,600,000
Unitil Service Corp.
Line of Credit Facility [Line Items]
Capital lease obligation, total capitalized cost						$ 13,400,000
Capital lease obligation, maturity period			Sep. 30, 2020
Capital lease obligation, current			$ 2,700,000
Capital lease obligation, noncurrent			3,000,000
Northern Utilities Inc
Line of Credit Facility [Line Items]
Natural gas storage inventory			9,600,000	9,000,000	8,500,000
Accounts Payable			100,000	100,000	3,100,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility			120,000,000	$ 120,000,000	$ 120,000,000
Proceeds from lines of credit			202,500,000
Repayments of lines of credit			$ 171,700,000
Credit Facility | Second Amended Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility	$ 120,000,000
Sublimit for the issuance of standby letters of credit	$ 25,000,000
Revolving credit facility termination date	Jul. 25, 2023
Increase in borrowing limit	$ 50,000,000
Credit Facility | Second Amended Credit Facility [Member] | London Interbank Offered Rate
Line of Credit Facility [Line Items]
Credit facility, daily fluctuating rate of interest	1.125%
Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Percentage of capitalization			The affirmative and negative covenants under the Credit Facility shall apply until the Credit Facility terminates and all amounts borrowed under the Credit Facility are paid in full (or with respect to letters of credit, they are cash collateralized). The only financial covenant in the Credit Facility provides that Funded Debt to Capitalization (as each term is defined in the Credit Facility) cannot exceed 65%, tested on a quarterly basis. At September 30, 2018, September 30, 2017 and December 31, 2017, the Company was in compliance with the covenants contained in the Credit Facility in effect on that date.
7.15% Senior Notes, Due December 15, 2018 | Granite State Gas Transmission Inc
Line of Credit Facility [Line Items]
Long-term debt, maturity date			Dec. 15, 2018	Dec. 15, 2018	Dec. 15, 2018
Long-term debt, stated interest rate			7.15%	7.15%	7.15%
Senior Notes			$ 3,300,000
3.52% Senior Notes, Due November 1, 2027 | Northern Utilities Inc
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount		$ 20,000,000
Long-term debt, maturity date		Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027
Long-term debt, stated interest rate		3.52%	3.52%	3.52%	3.52%
3.52% Senior Notes, Due November 1, 2027 | Fitchburg Gas and Electric Light Company
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount		$ 10,000,000
Long-term debt, maturity date		Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027
Long-term debt, stated interest rate		3.52%	3.52%	3.52%	3.52%
4.32% Senior Notes, Due November 1, 2047 | Northern Utilities Inc
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount		$ 30,000,000
Long-term debt, maturity date		Nov. 1, 2047	Nov. 1, 2047	Nov. 1, 2047	Nov. 1, 2047
Long-term debt, stated interest rate		4.32%	4.32%	4.32%	4.32%
4.32% Senior Notes, Due November 1, 2047 | Fitchburg Gas and Electric Light Company
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount		$ 15,000,000
Long-term debt, maturity date		Nov. 1, 2047	Nov. 1, 2047	Nov. 1, 2047	Nov. 1, 2047
Long-term debt, stated interest rate		4.32%	4.32%	4.32%	4.32%
3.72% Senior Notes, Due November 1, 2027 | Granite State Gas Transmission Inc
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount		$ 15,000,000
Long-term debt, maturity date		Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027	Nov. 1, 2027
Long-term debt, stated interest rate		3.72%	3.72%	3.72%	3.72%

Borrowing Limits Amounts Outsta

Borrowing Limits Amounts Outstanding and Amounts Available under Credit Facility (Detail) - USD ($)	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Debt Instrument [Line Items]
Short-Term Borrowings Outstanding	$ 69,100,000	$ 38,300,000	$ 111,900,000
Revolving Credit Facility
Debt Instrument [Line Items]
Credit facility, limit	120,000,000	120,000,000	120,000,000
Short-Term Borrowings Outstanding	69,100,000	38,300,000	111,900,000
Letters of Credit Outstanding			1,100,000
Available credit facility	$ 50,900,000	$ 81,700,000	$ 7,000,000

Common Stock And Preferred St_3

Common Stock And Preferred Stock - Additional Information (Detail) - USD ($)	Oct. 01, 2018	Jan. 29, 2018	Dec. 14, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, shares outstanding				14,872,011	14,119,893	14,872,011	14,119,893	14,815,585
Common stock, shares issued				5,423	6,173	19,700	20,564
Proceeds from Issuance of Common Stock						$ 900,000	$ 1,000,000
Share based compensation expense						$ 2,100,000	2,600,000
Percentage of fully-vested restricted stock units that directors will receive in common shares when settled						70.00%
Percentage of fully-vested restricted stock units that directors will receive in cash when settled						30.00%
Fair value of liabilities associated with fully vested RSUs that will be settled in cash				$ 1,200,000	$ 900,000	$ 1,200,000	900,000	$ 1,000,000
Preferred Stock				200,000	200,000	200,000	200,000	$ 200,000
Maximum
Class of Stock [Line Items]
Dividend declared				$ 100,000	$ 100,000	100,000	$ 100,000
Dividend and Distribution Reinvestment and Share Purchase Plan
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock						$ 925,000
Dividend and Distribution Reinvestment and Share Purchase Plan | Average
Class of Stock [Line Items]
Common stock price per share				$ 46.97		$ 46.97
Dividend and Distribution Reinvestment and Share Purchase Plan | Common Stock
Class of Stock [Line Items]
Common stock, shares issued						19,700
Registered Public Offering
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock			$ 31,700,000
Registered Public Offering | Common Stock
Class of Stock [Line Items]
Common stock, shares issued			690,000
Common stock price per share			$ 48.30
Unitil Energy Systems Inc | Series 6
Class of Stock [Line Items]
Preferred stock, outstanding				1,893	1,893	1,893	1,893	1,893
Preferred Stock				$ 200,000	$ 200,000	$ 200,000	$ 200,000	$ 200,000
Dividend rate						6.00%	6.00%	6.00%
Restricted Stock
Class of Stock [Line Items]
Restricted stock vesting period						4 years
Restricted stock non-vested				49,581	89,326	49,581	89,326
Restricted stock weighted average grant date fair value						$ 41.96	$ 39.54
Unrecognized share based compensation				$ 1,000,000		$ 1,000,000
Share compensation recognition period						2 years 6 months
Restricted Stock Units Granted		37,510
Aggregate Market Value		$ 1,600,000
Forfeitures under the stock plan						784
Cancellations under the stock plan						0
Restricted Stock | Maximum
Class of Stock [Line Items]
Restricted stock available for awards				677,500		677,500
Restricted stock that may be awarded in any one calendar year to any one participant				20,000		20,000
Restricted Stock | Vesting Annually
Class of Stock [Line Items]
Restricted stock vesting percentage annually						25.00%
Restricted Stock Units (RSUs)
Class of Stock [Line Items]
Restricted Stock Units Granted	11,275					0
Restricted stock units outstanding					44,343		44,343
Weighted-Average Stock Price					$ 33.72		$ 33.72

Restricted Stock Units Issued (

Restricted Stock Units Issued (Detail) - Restricted Stock Units (RSUs) - $ / shares	Oct. 01, 2018	Sep. 30, 2018
Restricted Stock Units
Beginning Restricted Stock Units	53,454	52,224
Restricted Stock Units Granted	11,275	0
Dividend Equivalents Earned		1,230
Restricted Stock Units Settled		0
Ending Restricted Stock Units		53,454
Weighted-Average Stock Price
Beginning Restricted Stock Units	$ 36.47	$ 36.22
Restricted Stock Units Granted		0
Dividend Equivalents Earned		46.87
Restricted Stock Units Settled		0
Ending Restricted Stock Units		$ 36.47

Regulatory Matters - Additional

Regulatory Matters - Additional Information (Detail)

May 01, 2019USD ($)

May 07, 2018USD ($)

May 02, 2018USD ($)

May 01, 2018USD ($)

Apr. 30, 2018USD ($)

Feb. 28, 2018USD ($)

Jan. 01, 2018USD ($)

Aug. 25, 2017MW

Aug. 01, 2017USD ($)

Apr. 20, 2017USD ($)

Dec. 31, 2017

Sep. 30, 2018USD ($)StateCustomerMW

Jun. 30, 2027MW

Dec. 31, 2025MWh

Dec. 31, 2022MWh

Jun. 01, 2018USD ($)

May 10, 2018USD ($)

Jun. 30, 2017MW

Jun. 23, 2017kW

Nov. 09, 2016MW

Regulatory Assets [Line Items]

Spending cap

$ 4,400,000

Annual revenue adjustment

$ 2,300,000

Power capacity facility for small customers | kW

100

Tax Year 2018

Regulatory Assets [Line Items]

Corporate income tax rate

21.00%

21.00%

Scenario Forecast

Regulatory Assets [Line Items]

Annual revenue adjustment

$ 2,200,000

Unitil Energy Systems Inc | New Hampshire

Regulatory Assets [Line Items]

Increase (decrease) in annual revenue

$ 300,000

Permanent rate increase

$ 4,100,000

Reduction of federal tax decrease

2,200,000

Reconciliation adjustment of recouped difference between temporary rates and final rates

1,400,000

Unitil Energy Systems Inc | New Hampshire | First Rate Step Adjustments

Regulatory Assets [Line Items]

Permanent rate increase

$ 900,000

Unitil Energy Systems Inc | New Hampshire | Second rate Step Adjustments [Member]

Regulatory Assets [Line Items]

Increase (decrease) in annual revenue

$ 3,300,000

Fitchburg Gas and Electric Light Company

Regulatory Assets [Line Items]

Increase (decrease) in annual revenue

$ 900,000

$ (0.008)

Description of percentage of sales in legislation

The legislation contains numerous provisions, including: a requirement that increases the pace at which the Class 1 Renewable Portfolio Standard requirement increases, from the current pace of an additional 1 percent of sales each year to an additional 2 percent of sales each year during the period from January 1, 2020 through December 31, 2029.

Number of states with electric distribution companies | State

3

Fitchburg Gas and Electric Light Company | Solar Generation

Regulatory Assets [Line Items]

Power generation facility | MW

1.3

Recovery amount

$ 300,000

Fitchburg Gas and Electric Light Company | Minimum | Offshore Wind Energy

Regulatory Assets [Line Items]

Power generation facility | MW

400

Fitchburg Gas and Electric Light Company | Maximum

Regulatory Assets [Line Items]

Power generation facility | MW

1,600

Fitchburg Gas and Electric Light Company | Solar Massachusetts Renewable Target Program | Solar Generation

Regulatory Assets [Line Items]

Power generation capacity | MW

1,600

Fitchburg Gas and Electric Light Company | Scenario Forecast

Regulatory Assets [Line Items]

Power generation capacity | MWh

1,000

9,450,000

Fitchburg Gas and Electric Light Company | Scenario Forecast | Offshore Wind Energy

Regulatory Assets [Line Items]

Power generation facility | MW

1,600

Northern Utilities Inc

Regulatory Assets [Line Items]

Increase (decrease) in annual revenue

$ 2,600,000

$ 3,200,000

$ 2,600,000

Increase in annual base rate

2.40%

Annual TIRA Adjustment

$ 1,100,000

TIRA initial term

Four years

Northern Utilities Inc | Revenue Offset [Member]

Regulatory Assets [Line Items]

Increase (decrease) in annual revenue

$ (1,700,000)

Northern Utilities Inc | Maine

Regulatory Assets [Line Items]

Increase (decrease) in annual revenue

$ 2,100,000

Percentage of approved return on equity

9.50%

Percentage of approved return on equity, reflecting on equity

50.00%

Percentage of approved return on equity, reflecting on debt

50.00%

Reduction of annual operating costs

$ 500,000

TIRA extended term

8 years

Construction completion period

3 years

Number of new customers | Customer

1,000

Potential regulated operating revenue

$ 1,000,000

Northern Utilities Inc | Maine | Second TAB program

Regulatory Assets [Line Items]

Number of new customers | Customer

2,000

Potential regulated operating revenue

$ 2,000,000

Northern Utilities Inc | Maine | Revenue Offset [Member]

Regulatory Assets [Line Items]

Increase (decrease) in annual revenue

$ 2,200,000

Environmental Matters - Additio

Environmental Matters - Additional Information (Detail) - Environmental Restoration Costs	9 Months Ended
	Sep. 30, 2018
Maine
Site Contingency [Line Items]
Amortization period for environmental costs	5 years
New Hampshire
Site Contingency [Line Items]
Amortization period for environmental costs	7 years

Company's Liability for Environ

Company's Liability for Environmental Obligations (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Environmental Exit Cost [Line Items]
Total Balance at Beginning of Period	$ 2.1	$ 1.9
Additions	0.6	0.5
Less: Payments / Reductions	0.6	0.2
Total Balance at End of Period	2.1	2.2
Less: Current Portion			$ 0.6	$ 0.5
Noncurrent Balance			1.5	1.7
Total Balance at End of period	2.1	2.2	2.1	2.2
Fitchburg Gas and Electric Light Company
Environmental Exit Cost [Line Items]
Total Balance at Beginning of Period	0.1	0.1
Less: Payments / Reductions	0.1
Total Balance at End of Period		0.1
Less: Current Portion				0.1
Total Balance at End of period	0.1	0.1		0.1
Northern Utilities Inc
Environmental Exit Cost [Line Items]
Total Balance at Beginning of Period	2	1.8
Additions	0.6	0.5
Less: Payments / Reductions	0.5	0.2
Total Balance at End of Period	2.1	2.1
Less: Current Portion			0.6	0.4
Noncurrent Balance			1.5	1.7
Total Balance at End of period	$ 2.1	$ 2.1	$ 2.1	$ 2.1

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Income Taxes [Line Items]
Net Operating Loss Carryforwards		$ 18.2
Alternative minimum tax credit carryforwards		3.4
Regulatory Liability	$ 58.1	60.1	$ 58.1	$ 15
Regulatory liability, expected flow back to customers		$ 47.1
Regulatory liability, expected pass back to ratepayers			1.8
Minimum
Income Taxes [Line Items]
Average Rate Assumption Method estimated flow back period		15 years
Maximum
Income Taxes [Line Items]
Average Rate Assumption Method estimated flow back period		20 years
Income Tax Related Liabilities
Income Taxes [Line Items]
Regulatory Liability	$ 48.9	$ 47.9	$ 48.9
Tax Year 2018
Income Taxes [Line Items]
Corporate federal income tax	21.00%	21.00%
Federal, Maine, Massachusetts, and New Hampshire Tax Authorities
Income Taxes [Line Items]
Tax examination description		The Company remains subject to examination by Federal, Maine, Massachusetts, and New Hampshire tax authorities for the tax periods ended December 31, 2015; December 31, 2016; and December 31, 2017.

Key Weighted Average Assumption

Key Weighted Average Assumptions Used in Determining Benefit Plan Costs and Obligations (Detail) - Benefit Plan Costs	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	3.60%	4.10%
Rate of Compensation Increase	3.00%	3.00%
Expected Long-term rate of return on plan assets	7.75%	7.75%
Health Care Cost Trend Rate Assumed for Next Year	7.50%	8.00%
Ultimate Health Care Cost Trend Rate	4.50%	4.00%
Year that Ultimate Health Care Cost Trend Rate is reached	2,024	2,025

Components of Retirement Plan C

Components of Retirement Plan Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 848	$ 824	$ 2,544	$ 2,471
Interest Cost	1,469	1,514	4,407	4,543
Expected Return on Plan Assets	(1,946)	(1,826)	(5,838)	(5,479)
Prior Service Cost Amortization	81	66	243	197
Actuarial Loss Amortization	1,447	1,165	4,341	3,496
Sub-total	1,899	1,743	5,697	5,228
Amounts Capitalized and Deferred	(962)	(932)	(2,590)	(2,402)
Net Periodic Benefit Cost Recognized	937	811	3,107	2,826
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service Cost	733	744	2,199	2,231
Interest Cost	852	978	2,554	2,935
Expected Return on Plan Assets	(409)	(337)	(1,227)	(1,010)
Prior Service Cost Amortization	327	350	981	1,049
Actuarial Loss Amortization	346	524	1,038	1,573
Sub-total	1,849	2,259	5,545	6,778
Amounts Capitalized and Deferred	(930)	(1,226)	(2,557)	(3,418)
Net Periodic Benefit Cost Recognized	919	1,033	2,988	3,360
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service Cost	122	115	366	345
Interest Cost	101	98	303	294
Prior Service Cost Amortization	47	47	141	141
Actuarial Loss Amortization	121	74	365	222
Sub-total	391	334	1,175	1,002
Amounts Capitalized and Deferred	(113)	(99)	(339)	(297)
Net Periodic Benefit Cost Recognized	$ 278	$ 235	$ 836	$ 705

Retirement Benefit Obligation_2

Retirement Benefit Obligations - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2018USD ($)
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions to benefit plan	$ 16,600,000
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Contributions to benefit plan	3,000,000
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Benefit payments under SERP Plan	87,500
Expected additional benefit payments for the remainder of 2018	$ 313,100