Unitil (UTL) 10-Q 26 Oct 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Oct. 23, 2017
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
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 Common Stock, Shares Outstanding		14,120,764

CONSOLIDATED STATEMENTS OF EARN

CONSOLIDATED STATEMENTS OF EARNINGS - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating Revenues
Gas	$ 25.1	$ 22.1	$ 131.9	$ 124.1
Electric	57.5	55.2	154.4	150.4
Other	1.4	1.5	4.5	4.6
Total Operating Revenues	84	78.8	290.8	279.1
Operating Expenses
Cost of Gas Sales	8.3	6.1	56.6	52.4
Cost of Electric Sales	32.7	29.6	84.3	84.3
Operation and Maintenance	17.8	15.5	53	48.6
Depreciation and Amortization	10.8	11.6	35.2	35.1
Taxes Other Than Income Taxes	4.9	4.9	15.6	14.7
Total Operating Expenses	74.5	67.7	244.7	235.1
Operating Income	9.5	11.1	46.1	44
Interest Expense, net	5.8	5.5	17.1	16.7
Other Expense, net		0.1	0.1	0.2
Income Before Income Taxes	3.7	5.5	28.9	27.1
Income Tax Expense	1.4	2	11.1	10.2
Net Income	$ 2.3	$ 3.5	$ 17.8	$ 16.9
Net Income Per Common Share (Basic and Diluted)	$ 0.16	$ 0.25	$ 1.27	$ 1.21
Weighted Average Common Shares Outstanding - (Basic and Diluted)	14.1	14	14.1	14
Dividends Declared Per Share of Common Stock	$ 0.360	$ 0.355	$ 1.080	$ 1.065

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Current Assets:
Cash and Cash Equivalents	$ 10.9	$ 5.8	$ 4.4
Accounts Receivable, net	45.8	52.9	43.1
Accrued Revenue	39.2	49.5	35.5
Exchange Gas Receivable	9.5	8.3	9.8
Refundable Taxes	1.8	1.7	1.3
Gas Inventory	0.7	0.6	0.6
Materials and Supplies	7.3	6.8	6.9
Prepayments and Other	6.8	6	6
Total Current Assets	122	131.6	107.6
Utility Plant:
Gas	646.7	629.5	597.7
Electric	454.6	437.9	424
Common	36	35.8	35.7
Construction Work in Progress	113	70.2	89.6
Total Utility Plant	1,250.3	1,173.4	1,147
Less: Accumulated Depreciation	303.6	290	286
Net Utility Plant	946.7	883.4	861
Other Noncurrent Assets:
Regulatory Assets	102	104.1	96.5
Other Assets	9.2	9.1	7.3
Total Other Noncurrent Assets	111.2	113.2	103.8
TOTAL ASSETS	1,179.9	1,128.2	1,072.4
Current Liabilities:
Accounts Payable	24.1	32.4	23.1
Short-Term Debt	111.9	81.9	36.9
Long-Term Debt, Current Portion	29.8	16.8	17
Regulatory Liabilities	15	10.4	13.2
Energy Supply Obligations	12.9	12	13.2
Environmental Obligations	0.5	0.4	0.3
Capital Lease Obligations	3.1	3	3.1
Interest Payable	6	3.9	6.3
Other Current Liabilities	13	16.1	13.2
Total Current Liabilities	216.3	176.9	126.3
Noncurrent Liabilities:
Retirement Benefit Obligations	155	149	127.8
Deferred Income Taxes, net	109.2	97.9	99.6
Cost of Removal Obligations	84.8	77	77.4
Regulatory Liabilities		2.6	3.7
Capital Lease Obligations	6.4	8.3	9
Environmental Obligations	1.7	1.5	2.7
Other Noncurrent Liabilities	4.6	5.1	3.8
Total Noncurrent Liabilities	361.7	341.4	324
Capitalization:
Long-Term Debt, Less Current Portion	303.6	316.8	335
Stockholders' Equity:
Common Equity (Authorized: 25,000,000 and Outstanding: 14,119,893, 14,060,147 and 14,065,230 Shares)	243.4	240.7	239.9
Retained Earnings	54.7	52.2	47
Total Common Stock Equity	298.1	292.9	286.9
Preferred Stock	0.2	0.2	0.2
Total Stockholders' Equity	298.3	293.1	287.1
Total Capitalization	601.9	609.9	622.1
Commitments and Contingencies (Notes 6 & 7)
TOTAL LIABILITIES AND CAPITALIZATION	$ 1,179.9	$ 1,128.2	$ 1,072.4

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Common Stock Authorized	25,000,000	25,000,000	25,000,000
Common Equity Outstanding	14,119,893	14,065,230	14,060,147

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating Activities:
Net Income	$ 17.8	$ 16.9
Adjustments to Reconcile Net Income to Cash Provided by Operating Activities:
Depreciation and Amortization	35.2	35.1
Deferred Tax Provision	11.2	12.8
Changes in Working Capital Items:
Accounts Receivable	7.1	6.7
Accrued Revenue	10.3	2.9
Exchange Gas Receivable	(1.2)	1.3
Regulatory Liabilities	4.6	(2.4)
Accounts Payable	(8.3)	(10.2)
Taxes Payable	(0.1)	(3.7)
Other Changes in Working Capital Items	(2.5)	2.2
Deferred Regulatory and Other Charges	(5.1)	(2.6)
Other, net	5.7	3.7
Cash Provided by Operating Activities	74.7	62.7
Investing Activities:
Property, Plant and Equipment Additions	(84.2)	(74.4)
Cash (Used in) Investing Activities	(84.2)	(74.4)
Financing Activities:
Proceeds from (Repayment of) Short-Term Debt, net	30	(5.1)
Repayment of Long-Term Debt	(0.4)	(0.5)
Issuance of Long-Term Debt		30
Decrease in Capital Lease Obligations	(1.8)	(2)
Net Increase (Decrease) in Exchange Gas Financing	1.1	(1)
Dividends Paid	(15.3)	(15)
Proceeds from Issuance of Common Stock, net	1	1
Cash Provided by Financing Activities	14.6	7.4
Net Increase (Decrease)in Cash and Cash Equivalents	5.1	(4.3)
Cash and Cash Equivalents at Beginning of Period	5.8	8.7
Cash and Cash Equivalents at End of Period	10.9	4.4
Supplemental Cash Flow Information:
Interest Paid	15.2	14.2
Income Taxes Paid		1.6
Payments on Capital Leases	2.5	2.6
Non-cash Investing Activity:
Capital Expenditures Included in Accounts Payable	$ 1.8	$ 1.4

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, 2015	$ 282.6	$ 237.5	$ 45.1
Net Income	16.9		16.9
Dividends on Common Shares	(15)		(15)
Stock Compensation Plans	1.4	1.4
Issuance of Common Shares, Value	1	1
Ending Balance at Sep. 30, 2016	286.9	239.9	47
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, Value	1	1
Ending Balance at Sep. 30, 2017	$ 298.1	$ 243.4	$ 54.7

CONSOLIDATED STATEMENTS OF CHA7

CONSOLIDATED STATEMENTS OF CHANGES IN COMMON STOCK EQUITY (Parenthetical) - shares	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Common stock, shares issued	20,564	24,697

SUMMARY OF SIGNIFICANT ACCOUNTI

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	9 Months Ended
	Sep. 30, 2017
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	NOTE 1 – SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Nature of Operations 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 subsidiary. Usource, Inc. and Usource L.L.C. (collectively, Usource) are wholly-owned subsidiaries of Unitil Resources. Usource provides brokering and advisory services to large commercial and industrial customers in the northeastern United States. Basis of Presentation – 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 – Allowance for Doubtful Accounts – The Allowance for Doubtful Accounts as of September 30, 2017, September 30, 2016 and December 31, 2016, which is included in Accounts Receivable, net on the accompanying unaudited consolidated balance sheets, was as follows: ($ millions) September 30, December 31, 2017 2016 2016 Allowance for Doubtful Accounts $ 1.5 $ 1.2 $ 1.1 Accrued Revenue – September 30, December 31, Accrued Revenue ($ millions) 2017 2016 2016 Regulatory Assets – Current $ 31.3 $ 28.0 $ 37.9 Unbilled Revenues 7.9 7.5 11.6 Total Accrued Revenue $ 39.2 $ 35.5 $ 49.5 Exchange Gas Receivable – September 30, December 31, Exchange Gas Receivable ($ millions) 2017 2016 2016 Northern Utilities $ 8.9 $ 9.3 $ 7.8 Fitchburg 0.6 0.5 0.5 Total Exchange Gas Receivable $ 9.5 $ 9.8 $ 8.3 Gas Inventory September 30, December 31, Gas Inventory ($ millions) 2017 2016 2016 Natural Gas $ 0.4 $ 0.3 $ 0.3 Propane 0.2 0.2 0.2 Liquefied Natural Gas & Other 0.1 0.1 0.1 Total Gas Inventory $ 0.7 $ 0.6 $ 0.6 Utility Plant – Regulatory Accounting – September 30, December 31, Regulatory Assets consist of the following ($ millions) 2017 2016 2016 Retirement Benefits $ 76.2 $ 64.6 $ 75.9 Energy Supply & Other Rate Adjustment Mechanisms 28.2 23.2 32.7 Deferred Storm Charges 6.8 11.0 9.6 Environmental 9.9 12.2 10.8 Income Taxes 6.7 7.7 7.3 Other 5.5 5.8 5.7 Total Regulatory Assets $ 133.3 $ 124.5 $ 142.0 Less: Current Portion of Regulatory Assets (1) 31.3 28.0 37.9 Regulatory Assets – noncurrent $ 102.0 $ 96.5 $ 104.1 (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) 2017 2016 2016 Rate Adjustment Mechanisms $ 11.6 $ 8.5 $ 6.2 Gas Pipeline Refund (Note 6) 3.4 8.4 6.8 Total Regulatory Liabilities 15.0 16.9 13.0 Less: Current Portion of Regulatory Liabilities 15.0 13.2 10.4 Regulatory Liabilities – noncurrent $ — $ 3.7 $ 2.6 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, 2017 are $1.4 million of deferred storm charges to be recovered over the next year and $7.4 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, 2017, September 30, 2016 and December 31, 2016 the Company had 1.2 billion, 2.9 billion and 2.0 billion cubic feet (BCF), respectively, outstanding in natural gas futures and options contracts under its hedging program. As of September 30, 2017, September 30, 2016 and December 31, 2016, the Company’s derivatives that are not designated as hedging instruments under FASB ASC 815-20 have a fair value of $0.1 million, $0.2 million and $0.4 million, respectively. Investments in Marketable Securities At September 30, 2017, September 30, 2016 and December 31, 2016, the fair value of the Company’s investments in these trading securities, which are recorded on the Consolidated Balance Sheets in Other Assets, were $3.4 million, $1.9 million and $1.9 million, respectively, as shown in the table below. These investments are valued based on quoted prices from active markets and are categorized in Level 1 as they are actively traded and no valuation adjustments have been applied. Changes in the fair value of these investments are recorded in Other Expense, net. September 30, December 31, Fair Value of Marketable Securities ($ millions) 2017 2016 2016 Equity Funds $ 1.9 $ 1.1 $ 1.1 Fixed Income Funds 1.5 0.8 0.8 Total Marketable Securities $ 3.4 $ 1.9 $ 1.9 Energy Supply Obligations – September 30, December 31, Energy Supply Obligations ($ millions) 2017 2016 2016 Current: Exchange Gas Obligation $ 8.9 $ 9.3 $ 7.8 Renewable Energy Portfolio Standards 3.7 3.6 3.9 Power Supply Contract Divestitures 0.3 0.3 0.3 Total Energy Supply Obligations – Current 12.9 13.2 12.0 Noncurrent: Power Supply Contract Divestitures 1.0 1.4 1.3 Total Energy Supply Obligations $ 13.9 $ 14.6 $ 13.3 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 – In May 2017, the FASB issued Accounting Standards Update ASU No. 2017-09, “Compensation – Stock Compensation (Topic 718) – Scope of Modification Accounting”, to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new standard, modification is required only if the fair value, the vesting conditions, or the classification of an award as equity or liability changes as a result of the change in terms or conditions. The amendments are effective for all entities for annual periods beginning after December 15, 2017, including interim periods within those annual periods, and will be applied prospectively. Early adoption is permitted. The Company adopted this new guidance and it did not have a material impact on the Company’s Consolidated Financial Statements. In March 2017, the FASB issued ASU No. 2017-07, “Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.” The ASU amends the existing guidance relating to the presentation of net periodic pension cost and net periodic postretirement benefit cost. The amendment requires an employer to disaggregate the service cost component from the other components of net benefit cost and provides explicit guidance on how to present the service cost component and other components in the income statement. In addition, on a prospective basis, the ASU limits the component of net benefit cost eligible to be capitalized to service costs. The ASU will be effective for the Company on January 1, 2018, with early adoption permitted. Although the Company is currently evaluating the impact the guidance will have on the Consolidated Financial Statements and related disclosures, it is not expected to have a material impact to financial results. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, Topic 606, which amends existing revenue recognition guidance, effective January 1, 2018. The objective of the new standard is to provide a single, comprehensive revenue recognition model for all contracts with customers to improve comparability across entities, industries, jurisdictions, and capital markets and to provide more useful information to users of financial statements through improved and expanded disclosure requirements. 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 intends to use the modified retrospective method when adopting the new standard on January 1, 2018. The Company expects that the impact of the new guidance will be immaterial to the Consolidated Financial Statements. Upon adoption of ASU 2014-09, the Company plans to disclose revenues from contracts with customers separately from rate adjustment mechanism revenue. In March 2016, the FASB issued ASU 2016-09, which provides for improvements to employee share-based payment accounting. ASU 2016-09 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. ASU 2016-09 simplifies several aspects of the accounting for employee share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The Company adopted this new guidance in the first quarter of 2017 and it did not have an impact on the Company’s Consolidated Financial Statements. In February 2016, the FASB issued ASU 2016-02, Leases, Topic 842, which for lessees requires balance sheet recognition of right-of-use assets and lease liabilities for most leases. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2018. The Company has not yet fully determined the impacts of implementation. However, adoption is expected to occur on Jan. 1, 2019 utilizing the practical expedients provided by the standard. As such, agreements entered into prior to Jan. 1, 2017 that are currently considered leases are expected to be recognized on the consolidated balance sheet, including contracts for use of office space and equipment. The Company expects that similar agreements entered into after December 31, 2016 will generally qualify as leases under the new standard, but has not yet completed its evaluation of certain other contracts, including arrangements for the secondary use of assets, such as land easements. In January 2016, the FASB issued Accounting Standards Update (ASU) 2016-01 which addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments. A financial instrument is defined as cash, evidence of ownership interest in a company or other entity, or a contract that both: (i) imposes on one entity a contractual obligation either to deliver cash or another financial instrument to a second entity or to exchange other financial instruments on potentially unfavorable terms with the second entity and (ii) conveys to that second entity a contractual right either to receive cash or another financial instruments from the first entity or to exchange other financial instruments on potentially favorable terms with the first entity. This pronouncement is effective for financial statements issued for annual periods beginning after December 15, 2017 and interim periods within those annual periods with earlier application permitted as of the beginning of the fiscal year of adoption. The Company is evaluating the impact that this new guidance will have on the Company’s Consolidated Financial Statements. 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, 2017
DIVIDENDS DECLARED PER SHARE	NOTE 2 – DIVIDENDS DECLARED PER SHARE Declaration Date Date Paid (Payable) Shareholder of Record Date Dividend Amount 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 10/19/16 11/28/16 11/14/16 $0.355 07/20/16 08/26/16 08/12/16 $0.355 04/20/16 05/27/16 05/13/16 $ 0.355 01/27/16 02/26/16 02/12/16 $ 0.355

SEGMENT INFORMATION

SEGMENT INFORMATION	9 Months Ended
	Sep. 30, 2017
SEGMENT INFORMATION	NOTE 3 – SEGMENT INFORMATION The following table provides significant segment financial data for the three and nine months ended September 30, 2017 and September 30, 2016 and as of December 31, 2016 (millions): Gas Electric Non- Regulated Other Total 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 Three Months Ended September 30, 2016 Revenues $ 22.1 $ 55.2 $ 1.5 $ — $ 78.8 Segment Profit (Loss) (2.2 ) 5.3 0.3 0.1 3.5 Capital Expenditures 22.9 8.8 — 3.1 34.8 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 Nine Months Ended September 30, 2016 Revenues $ 124.1 $ 150.4 $ 4.6 $ — $ 279.1 Segment Profit 7.2 8.7 0.9 0.1 16.9 Capital Expenditures 44.8 21.8 — 7.8 74.4 Segment Assets 610.3 425.4 7.2 29.5 1,072.4 As of December 31, 2016 Segment Assets $ 645.2 $ 441.1 $ 6.8 $ 35.1 $ 1,128.2

DEBT AND FINANCING ARRANGEMENTS

DEBT AND FINANCING ARRANGEMENTS	9 Months Ended
	Sep. 30, 2017
DEBT AND FINANCING ARRANGEMENTS	NOTE 4 – DEBT AND FINANCING ARRANGEMENTS Details on long-term debt at September 30, 2017, September 30, 2016 and December 31, 2016 are shown below: ($ millions) September 30, December 31, 2017 2016 2016 Unitil Corporation Senior Notes: 6.33% Notes, Due May 1, 2022 $ 20.0 $ 20.0 $ 20.0 3.70% Notes, Due August 1, 2026 30.0 30.0 30.0 Unitil Energy Systems, Inc.: First Mortgage Bonds: 5.24% Series, Due March 2, 2020 15.0 15.0 15.0 8.49% Series, Due October 14, 2024 9.0 12.0 9.0 6.96% Series, Due September 1, 2028 20.0 20.0 20.0 8.00% Series, Due May 1, 2031 15.0 15.0 15.0 6.32% Series, Due September 15, 2036 15.0 15.0 15.0 Fitchburg Gas and Electric Light Company: Long-Term Notes: 6.75% Notes, Due November 30, 2023 9.5 11.4 9.5 6.79% Notes, Due October 15, 2025 10.0 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 Northern Utilities Senior Notes: 6.95% Senior Notes, Series A, Due December 3, 2018 20.0 30.0 20.0 5.29% Senior Notes, Due March 2, 2020 25.0 25.0 25.0 7.72% Senior Notes, Series B, Due December 3, 2038 50.0 50.0 50.0 4.42% Senior Notes, Due October 15, 2044 50.0 50.0 50.0 Granite State Senior Notes: 7.15% Senior Notes, Due December 15, 2018 6.7 10.0 6.7 Unitil Realty Corp.: Senior Secured Notes: 8.00% Notes, Due Through August 1, 2017 — 0.6 0.4 Total Long-Term Debt 336.2 355.0 336.6 Less: Unamortized Debt Issuance Costs 2.8 3.0 3.0 Total Long-Term Debt, net of Unamortized Debt Issuance Costs 333.4 352.0 333.6 Less: Current Portion 29.8 17.0 16.8 Total Long-term Debt, Less Current Portion $ 303.6 $ 335.0 $ 316.8 Fair Value of Long-Term Debt ($ millions) September 30, December 31, 2017 2016 2016 Estimated Fair Value of Long-Term Debt $ 383.0 $ 405.8 $ 370.3 Credit Arrangements On October 4, 2013, the Company entered into an Amended and Restated Credit Agreement (as further amended, restated, amended and restated, modified or supplemented from time to time, the “Credit Facility”). The Credit Facility terminates October 4, 2020 and provides for a borrowing limit of $120 million which includes a $25 million sublimit for the issuance of standby letters of credit. The Credit Facility provides Unitil with the ability to elect that borrowings under the Credit Facility bear interest under several options, including at a daily fluctuating rate of interest per annum equal to one-month London Interbank Offered Rate (LIBOR) plus 1.25%. Provided there is no event of default under the Credit Facility, the Company may on a one-time basis request an increase in the aggregate commitments under the Credit Facility by an aggregate additional amount of up to $30 million. The Company utilizes the Credit Facility for cash management purposes related to its short-term operating activities. Total gross borrowings were $164.2 million for the nine months ended September 30, 2017. Total gross repayments were $134.2 million for the nine months ended September 30, 2017. The following table details the borrowing limits, amounts outstanding and amounts available under the revolving Credit Facility as of September 30, 2017, September 30, 2016 and December 31, 2016: Revolving Credit Facility ($ millions) September 30, December 31, 2017 2016 2016 Limit $ 120.0 $ 120.0 $ 120.0 Short-Term Borrowings Outstanding $ 111.9 $ 36.9 $ 81.9 Letters of Credit Outstanding $ 1.1 $ 1.1 $ 1.1 Available $ 7.0 $ 82.0 $ 37.0 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, Unitil Corporation’s and its subsidiaries’ ability to permit liens or incur indebtedness, and restrictions on Unitil’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, 2017, September 30, 2016 and December 31, 2016, the Company was in compliance with the covenants contained in the Credit Facility in effect on that date. The weighted average interest rates on all short-term borrowings and intercompany money pool transactions were 2.3% and 1.7% for the nine months ended September 30, 2017 and September 30, 2016, respectively. The weighted average interest rate on all short-term borrowings for the twelve months ended December 31, 2016 was 1.8%. 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. On July 14, 2017, Northern Utilities, Fitchburg and Granite State, entered into agreements to issue and sell $90 million collectively of Senior Unsecured Notes (Notes) through a private placement marketing process to institutional investors. Northern Utilities priced $20 million of Notes due 2027 at 3.52% and $30 million of Notes due 2047 at 4.32%. Fitchburg priced $10 million of Notes due 2027 at 3.52% and $15 million of Notes due 2047 at 4.32%. Granite State priced $15 million of Notes due 2027 at 3.72%. Northern Utilities, Fitchburg and Granite State plan to use the net proceeds from the offering to repay short-term debt and for general corporate purposes and anticipate closing and funding this long-term financing on November 1, 2017. However, the issuance of the Notes is subject to customary closing conditions for a transaction of this type. The Notes offered have not been and will not be registered under the Securities Act of 1933 (Act), or any state securities laws, and may not be offered or sold in the United States absent registration or an applicable exemption from the registration requirements of the Act and applicable state securities laws. As of September 30, 2017, the Company has deferred $0.1 million of costs associated with this financing. In April 2014, Unitil Service 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, 2017, there are $2.7 million of current and $5.8 million of noncurrent obligations under this capital lease on the Company’s Consolidated Balance Sheets. 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 $9.0 million, $9.3 million and $9.9 million of natural gas storage inventory at September 30, 2017, September 30, 2016 and December 31, 2016, respectively, related to these asset management agreements. The amount of natural gas inventory released in September 2017 and payable in October 2017 is $0.1 million and is recorded in Accounts Payable at September 30, 2017. The amount of natural gas inventory released in September 2016 and payable in October 2016 was $0.1 million and is recorded in Accounts Payable at September 30, 2016. The amount of natural gas inventory released in December 2016 and payable in January 2017 was $2.1 million and was recorded in Accounts Payable at December 31, 2016. 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, 2017, there were approximately $19.8 million of guarantees outstanding and the longest term guarantee extends through August 2018. The Company also guarantees the payment of principal, interest and other amounts payable on the notes issued by Granite State. As of September 30, 2017, the principal amount outstanding for the 7.15% Granite State notes was $6.7 million.

COMMON STOCK AND PREFERRED STOC

COMMON STOCK AND PREFERRED STOCK	9 Months Ended
	Sep. 30, 2017
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 14,060,147,14,065,230 and 14,119,893 shares of common stock outstanding at September 30, 2016, December 31, 2016 and September 30, 2017, respectively. 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 30, 2017, 34,930 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 89,326 and 95,506 non-vested shares under the Stock Plan as of September 30, 2017 and 2016, respectively. The weighted average grant date fair value of these shares was $39.54 and $35.30, respectively. The compensation expense associated with the issuance of shares under the Stock Plan is being recognized over the vesting period and was $2.6 million and $2.0 million for the nine months ended September 30, 2017 and 2016, respectively. At September 30, 2017, there was approximately $1.0 million of total unrecognized compensation cost under the Stock Plan which is expected to be recognized over approximately 2.4 years. There were 831 Restricted Shares forfeited and no cancellations under the Stock Plan during the nine months ended September 30, 2017. Restricted Stock Units Non-management members of the Company’s Board of Directors (Directors) may elect to receive the equity portion of their annual retainer in the form of Restricted Stock Units. Restricted Stock Units earn dividend equivalents and will generally be settled by payment to each Director as soon as practicable following the Director’s separation from service to the Company. The Restricted Stock Units will be paid such that the Director will receive (i) 70% of the shares of the Company’s common stock underlying the restricted stock units and (ii) cash in an amount equal to the fair market value of 30% of the shares of the Company’s common stock underlying the Restricted Stock Units. The equity portion of Restricted Stock Units activity during the nine months ended September 30, 2017 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, 2016 43,345 $ 33.40 Restricted Stock Units Granted — — Dividend Equivalents Earned 998 $ 47.32 Restricted Stock Units Settled — — Restricted Stock Units as of September 30, 2017 44,343 $ 33.72 There were 34,498 Restricted Stock Units outstanding as of September 30, 2016 with a weighted average stock price of $32.03. On October 2, 2017, there were 10,746 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, 2017, September 30, 2016 and December 31, 2016 is $0.9 million, $0.6 million and $0.8 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, 2017 and December 31, 2016. There was $0.2 million, or 1,893 shares, of Unitil Energy’s 6.00% Series Preferred Stock outstanding as of September 30, 2016. 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, 2017 and September 30, 2016, respectively.

REGULATORY MATTERS

REGULATORY MATTERS	9 Months Ended
	Sep. 30, 2017
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 FOR DECEMBER 31, 2016 AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON FEBRUARY 2, 2017. Rate Case Activity Unitil Energy – Base Rates Fitchburg – Base Rates – Electric – Fitchburg – Base Rates – Gas – Fitchburg – Gas Operations – Northern Utilities – Base Rates – Maine – In addition to the distribution base rate increase, Northern Utilities is requesting to extend its Targeted Infrastructure Replacement Adjustment mechanism (TIRA). The TIRA is a capital cost recovery mechanism designed to recover the annual revenue requirements associated with targeted investments in gas distribution system infrastructure replacement and upgrade projects, including the Company’s Cast Iron Replacement Program (CIRP). This matter remains pending. Northern Utilities – Targeted Infrastructure Replacement Adjustment – Northern Utilities – Targeted Area Build-out Program – Maine – Northern Utilities – Base Rates – New Hampshire – Northern Utilities reached a settlement agreement on temporary rates to produce an increase in annual revenues of approximately $1.6 million, effective with service rendered on and after August 1, 2017, and until a final, non-appealable order on permanent rates is issued. As of September 30, 2017, Northern Utilities has deferred approximately $0.3 million of costs associated with this base rate case. Once a final decision on permanent rates is issued, it will be reconciled back to the date that temporary rates were implemented. The settlement agreement was approved by the Commission on July 31, 2017. In its initial petition, Northern Utilities requested approval to implement a multi-year rate plan, including a capital cost recovery mechanism, which will allow for recovery of the revenue requirements associated with future annual capital expenditures as defined under the plan through changes, or step adjustments, to Northern Utilities’ distribution rates without the need to file a general rate case prior to January 2021. This matter remains pending. Northern Utilities – Pipeline Refund – Granite State – Base Rates – Other Matters NHPUC Energy Efficiency Resource Standard Proceeding – Unitil Energy – Electric Grid Modernization – Unitil Energy – Net Metering – Fitchburg – Electric Operations – Fitchburg – Service Quality – Fitchburg – Solar Generation – Fitchburg – Energy Diversity – Fitchburg – Clean Energy RFP – Fitchburg – Other – On May 11, 2016, the MDPU issued an Order commencing a rulemaking proceeding to adopt emergency regulations amending 220 C.M.R. § 18.00 et seq. (“Net Metering Regulations”). Specifically, the MDPU amended its Net Metering Regulations to implement the net metering provisions of An Act Relative to Solar Energy, St. 2016, c. 75, §§ 3-9, and to make additional clerical changes to the Net Metering Regulations. On July 15, 2016, the MDPU issued an order approving Final Net Metering Regulations. Fitchburg’s tariff, filed in compliance with the new regulations, was approved on February 7, 2017. In December 2013, the MDPU opened an investigation into Modernization of the Electric Grid. The stated objective of the Grid Modernization proceeding is to ensure that the electric distribution companies “adopt grid modernization policies and practices.” In June 2014, the MDPU issued its first Grid Modernization order, setting forth a requirement that each electric distribution company submit a ten-year strategic Grid Modernization Plan (GMP). As part of the GMP, each company must include a five-year Short-Term Investment Plan (STIP), which must include an approach to achieving advanced metering functionality within five years of the Department’s approval of the GMP. The filing of a GMP is a recurring obligation and must be updated as part of subsequent base distribution rate cases, which by statute must occur no less often than every five years. Capital investments contained in the STIP are eligible for pre-authorization, meaning that the MDPU will not revisit in later filings whether the Company should have proceeded with these investments. Fitchburg and the Commonwealth’s three other electric distribution companies filed their initial GMPs on August 19, 2015. These filings are currently under MDPU review and remain pending. On January 28, 2016 the MDPU approved Fitchburg’s Three-Year Energy Efficiency Plan for 2016-2018, subject to limited modifications and directives in the Order. The Department found that the savings goals included in each Three-Year Plan are reasonable and are consistent with the achievement of all available cost-effective energy efficiency; approved each Program Administrator’s program implementation cost budget for the Three-Year Plans; approved the performance incentive pool, mechanism, and payout rates; found that all proposed energy efficiency programs are cost-effective; found that funding sources are reasonable and that each Program Administrator may recover the funds to implement its energy efficiency plan through its Energy Efficiency Surcharge; and found that each Program Administrator’s Three-Year Plan is consistent with the Green Communities Act, the Guidelines, and Department precedent. FERC Transmission Formula Rate Proceedings – 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 (the “Court”), (captioned Bellermann et al v. Fitchburg Gas and Electric Light Company). The Complaint seeks 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 that this suit is without merit and will continue to defend itself vigorously. Based upon information furnished by counsel and others, the Company believes that the ultimate resolution of this suit will not have a material impact on its financial position, operating results or cash flows. The Town of Lunenburg filed a separate action in the Court arising out of the December 2008 ice storm. The Court granted the Company’s Motion for Summary Judgment on all counts in December 2016 and dismissed the Town’s complaint. The Town filed a notice of appeal, but failed to perfect its appeal with the Court in a timely manner. A motion to dismiss for failure to perfect the appeal was granted by the Massachusetts Appeals Court in August 2017.

ENVIRONMENTAL MATTERS

ENVIRONMENTAL MATTERS	9 Months Ended
	Sep. 30, 2017
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 FOR DECEMBER 31, 2016 AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON FEBRUARY 2, 2017. 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, 2017, has not identified any material losses reasonably likely to be incurred in excess of recorded amounts. However, we 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 – Northern Utilities has worked with the Maine Department of Environmental Protection (ME DEP) and New Hampshire Department of Environmental Services (NH DES) to address environmental concerns with these sites. Northern Utilities or others have substantially completed remediation of the Exeter, Rochester, Dover, Somersworth, Portsmouth, Lewiston, Portland and Scarborough sites, though on site monitoring continues and it is possible that future activities may be required. 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, 2017 and 2016. Environmental Obligations ($ millions) Fitchburg Northern Total Nine months ended September 30, 2017 2016 2017 2016 2017 2016 Total Balance at Beginning of Period $ 0.1 $ 1.2 $ 1.8 $ 1.6 $ 1.9 $ 2.8 Additions — — 0.5 0.9 0.5 0.9 Less: Payments / Reductions — 0.1 0.2 0.6 0.2 0.7 Total Balance at End of Period 0.1 1.1 2.1 1.9 2.2 3.0 Less: Current Portion 0.1 0.1 0.4 0.2 0.5 0.3 Noncurrent Balance at End of Period $ — $ 1.0 $ 1.7 $ 1.7 $ 1.7 $ 2.7

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2017
INCOME TAXES	NOTE 8: INCOME TAXES The Company filed its tax returns for the year ended December 31, 2016 with the Internal Revenue Service in September 2017 and generated additional federal net operating loss (NOL) carryforward assets principally due to current tax repair deductions, tax depreciation and research and development deductions. As of September 30, 2017, the Company had recorded cumulative federal and state NOL carryforward assets of $23.9 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, 2017, 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. The Company evaluated its tax positions at September 30, 2017 in accordance with the FASB Codification, and has concluded that no adjustment for recognition, derecognition, settlement and foreseeable future events to any tax liabilities or assets as defined by the FASB Codification is required. The Company remains subject to examination by Federal, Maine, Massachusetts, and New Hampshire tax authorities for the tax periods ended December 31, 2014; December 31, 2015; and December 31, 2016. The Company received notice that its Maine income tax return filings for the years ended December 31, 2014; December 31, 2015; and December 31, 2016 are under examination by the Maine Revenue Service. Auditor fieldwork is scheduled to occur in the fourth quarter of 2017 and the Company does not expect that the results of this examination will have a material impact on its financial position, operating results or cash flows. 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, 2017
RETIREMENT BENEFIT OBLIGATIONS	NOTE 9: RETIREMENT BENEFIT OBLIGATIONS The Company co-sponsors the Unitil Corporation Retirement Plan (Pension Plan), the Unitil Retiree Health and Welfare Benefits Plan (PBOP Plan), and the Unitil Corporation Supplemental Executive Retirement Plan (SERP) to provide certain pension and postretirement benefits for its retirees and current employees. Please see Note 10 to the Consolidated Financial Statements in the Company’s Form 10-K for the year ended December 31, 2016 as filed with the SEC on February 2, 2017 for additional information regarding these plans. The following table includes the key weighted average assumptions used in determining the Company’s benefit plan costs and obligations: 2017 2016 Used to Determine Plan Costs Discount Rate 4.10 % 4.30 % Rate of Compensation Increase 3.00 % 3.00 % Expected Long-term rate of return on plan assets 7.75 % 8.00 % Health Care Cost Trend Rate Assumed for Next Year 8.00 % 7.00 % Ultimate Health Care Cost Trend Rate 4.00 % 4.00 % Year that Ultimate Health Care Cost Trend Rate is reached 2025 2022 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, 2017 2016 2017 2016 2017 2016 Service Cost $ 824 $ 851 $ 744 $ 652 $ 115 $ 41 Interest Cost 1,514 1,486 978 808 98 96 Expected Return on Plan Assets (1,826 ) (1,814 ) (337 ) (301 ) — — Prior Service Cost Amortization 66 66 350 372 47 47 Actuarial Loss Amortization 1,165 1,099 524 262 74 94 Sub-total 1,743 1,688 2,259 1,793 334 278 Amounts Capitalized and Deferred (932 ) (839 ) (1,226 ) (904 ) — — Net Periodic Benefit Cost Recognized $ 811 $ 849 $ 1,033 $ 889 $ 334 $ 278 Pension Plan PBOP Plan SERP Nine Months Ended September 30, 2017 2016 2017 2016 2017 2016 Service Cost $ 2,471 $ 2,553 $ 2,231 $ 1,956 $ 345 $ 123 Interest Cost 4,543 4,458 2,935 2,424 294 288 Expected Return on Plan Assets (5,479 ) (5,442 ) (1,010 ) (903 ) — — Prior Service Cost Amortization 197 198 1,049 1,116 141 141 Actuarial Loss Amortization 3,496 3,297 1,573 786 222 282 Sub-total 5,228 5,064 6,778 5,379 1,002 834 Amounts Capitalized and Deferred (2,402 ) (2,246 ) (3,418 ) (2,508 ) — — Net Periodic Benefit Cost Recognized $ 2,826 $ 2,818 $ 3,360 $ 2,871 $ 1,002 $ 834 Employer Contributions As of September 30, 2017, the Company had made $4.1 million and $2.8 million of contributions to its Pension Plan and PBOP Plan, respectively, in 2017. The Company, along with its subsidiaries, expects to continue to make contributions to its Pension and PBOP Plans in 2017 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, 2017, the Company had made $25,600 of benefit payments under the SERP Plan in 2017. The Company presently anticipates making an additional $8,500 of benefit payments under the SERP Plan in 2017.

SUMMARY OF SIGNIFICANT ACCOUN17

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	9 Months Ended
	Sep. 30, 2017
Nature of Operations	Nature of Operations 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 subsidiary. Usource, Inc. and Usource L.L.C. (collectively, Usource) are wholly-owned subsidiaries of Unitil Resources. Usource provides brokering and advisory services to large commercial and industrial customers in the northeastern United States.
Basis of Presentation	Basis of Presentation –
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 –
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts – The Allowance for Doubtful Accounts as of September 30, 2017, September 30, 2016 and December 31, 2016, which is included in Accounts Receivable, net on the accompanying unaudited consolidated balance sheets, was as follows: ($ millions) September 30, December 31, 2017 2016 2016 Allowance for Doubtful Accounts $ 1.5 $ 1.2 $ 1.1
Accrued Revenue	Accrued Revenue – September 30, December 31, Accrued Revenue ($ millions) 2017 2016 2016 Regulatory Assets – Current $ 31.3 $ 28.0 $ 37.9 Unbilled Revenues 7.9 7.5 11.6 Total Accrued Revenue $ 39.2 $ 35.5 $ 49.5
Exchange Gas Receivable	Exchange Gas Receivable – September 30, December 31, Exchange Gas Receivable ($ millions) 2017 2016 2016 Northern Utilities $ 8.9 $ 9.3 $ 7.8 Fitchburg 0.6 0.5 0.5 Total Exchange Gas Receivable $ 9.5 $ 9.8 $ 8.3
Gas Inventory	Gas Inventory September 30, December 31, Gas Inventory ($ millions) 2017 2016 2016 Natural Gas $ 0.4 $ 0.3 $ 0.3 Propane 0.2 0.2 0.2 Liquefied Natural Gas & Other 0.1 0.1 0.1 Total Gas Inventory $ 0.7 $ 0.6 $ 0.6
Utility Plant	Utility Plant –
Regulatory Accounting	Regulatory Accounting – September 30, December 31, Regulatory Assets consist of the following ($ millions) 2017 2016 2016 Retirement Benefits $ 76.2 $ 64.6 $ 75.9 Energy Supply & Other Rate Adjustment Mechanisms 28.2 23.2 32.7 Deferred Storm Charges 6.8 11.0 9.6 Environmental 9.9 12.2 10.8 Income Taxes 6.7 7.7 7.3 Other 5.5 5.8 5.7 Total Regulatory Assets $ 133.3 $ 124.5 $ 142.0 Less: Current Portion of Regulatory Assets (1) 31.3 28.0 37.9 Regulatory Assets – noncurrent $ 102.0 $ 96.5 $ 104.1 (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) 2017 2016 2016 Rate Adjustment Mechanisms $ 11.6 $ 8.5 $ 6.2 Gas Pipeline Refund (Note 6) 3.4 8.4 6.8 Total Regulatory Liabilities 15.0 16.9 13.0 Less: Current Portion of Regulatory Liabilities 15.0 13.2 10.4 Regulatory Liabilities – noncurrent $ — $ 3.7 $ 2.6 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, 2017 are $1.4 million of deferred storm charges to be recovered over the next year and $7.4 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, 2017, September 30, 2016 and December 31, 2016 the Company had 1.2 billion, 2.9 billion and 2.0 billion cubic feet (BCF), respectively, outstanding in natural gas futures and options contracts under its hedging program. As of September 30, 2017, September 30, 2016 and December 31, 2016, the Company’s derivatives that are not designated as hedging instruments under FASB ASC 815-20 have a fair value of $0.1 million, $0.2 million and $0.4 million, respectively.
Investments in Marketable Securities	Investments in Marketable Securities At September 30, 2017, September 30, 2016 and December 31, 2016, the fair value of the Company’s investments in these trading securities, which are recorded on the Consolidated Balance Sheets in Other Assets, were $3.4 million, $1.9 million and $1.9 million, respectively, as shown in the table below. These investments are valued based on quoted prices from active markets and are categorized in Level 1 as they are actively traded and no valuation adjustments have been applied. Changes in the fair value of these investments are recorded in Other Expense, net. September 30, December 31, Fair Value of Marketable Securities ($ millions) 2017 2016 2016 Equity Funds $ 1.9 $ 1.1 $ 1.1 Fixed Income Funds 1.5 0.8 0.8 Total Marketable Securities $ 3.4 $ 1.9 $ 1.9
Energy Supply Obligations	Energy Supply Obligations – September 30, December 31, Energy Supply Obligations ($ millions) 2017 2016 2016 Current: Exchange Gas Obligation $ 8.9 $ 9.3 $ 7.8 Renewable Energy Portfolio Standards 3.7 3.6 3.9 Power Supply Contract Divestitures 0.3 0.3 0.3 Total Energy Supply Obligations – Current 12.9 13.2 12.0 Noncurrent: Power Supply Contract Divestitures 1.0 1.4 1.3 Total Energy Supply Obligations $ 13.9 $ 14.6 $ 13.3 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 – In May 2017, the FASB issued Accounting Standards Update ASU No. 2017-09, “Compensation – Stock Compensation (Topic 718) – Scope of Modification Accounting”, to clarify when to account for a change to the terms or conditions of a share-based payment award as a modification. Under the new standard, modification is required only if the fair value, the vesting conditions, or the classification of an award as equity or liability changes as a result of the change in terms or conditions. The amendments are effective for all entities for annual periods beginning after December 15, 2017, including interim periods within those annual periods, and will be applied prospectively. Early adoption is permitted. The Company adopted this new guidance and it did not have a material impact on the Company’s Consolidated Financial Statements. In March 2017, the FASB issued ASU No. 2017-07, “Compensation – Retirement Benefits (Topic 715): Improving the Presentation of Net Periodic Pension Cost and Net Periodic Postretirement Benefit Cost.” The ASU amends the existing guidance relating to the presentation of net periodic pension cost and net periodic postretirement benefit cost. The amendment requires an employer to disaggregate the service cost component from the other components of net benefit cost and provides explicit guidance on how to present the service cost component and other components in the income statement. In addition, on a prospective basis, the ASU limits the component of net benefit cost eligible to be capitalized to service costs. The ASU will be effective for the Company on January 1, 2018, with early adoption permitted. Although the Company is currently evaluating the impact the guidance will have on the Consolidated Financial Statements and related disclosures, it is not expected to have a material impact to financial results. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers, Topic 606, which amends existing revenue recognition guidance, effective January 1, 2018. The objective of the new standard is to provide a single, comprehensive revenue recognition model for all contracts with customers to improve comparability across entities, industries, jurisdictions, and capital markets and to provide more useful information to users of financial statements through improved and expanded disclosure requirements. 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 intends to use the modified retrospective method when adopting the new standard on January 1, 2018. The Company expects that the impact of the new guidance will be immaterial to the Consolidated Financial Statements. Upon adoption of ASU 2014-09, the Company plans to disclose revenues from contracts with customers separately from rate adjustment mechanism revenue. In March 2016, the FASB issued ASU 2016-09, which provides for improvements to employee share-based payment accounting. ASU 2016-09 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. ASU 2016-09 simplifies several aspects of the accounting for employee share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The Company adopted this new guidance in the first quarter of 2017 and it did not have an impact on the Company’s Consolidated Financial Statements. In February 2016, the FASB issued ASU 2016-02, Leases, Topic 842, which for lessees requires balance sheet recognition of right-of-use assets and lease liabilities for most leases. This guidance will be effective for interim and annual reporting periods beginning after Dec. 15, 2018. The Company has not yet fully determined the impacts of implementation. However, adoption is expected to occur on Jan. 1, 2019 utilizing the practical expedients provided by the standard. As such, agreements entered into prior to Jan. 1, 2017 that are currently considered leases are expected to be recognized on the consolidated balance sheet, including contracts for use of office space and equipment. The Company expects that similar agreements entered into after December 31, 2016 will generally qualify as leases under the new standard, but has not yet completed its evaluation of certain other contracts, including arrangements for the secondary use of assets, such as land easements. In January 2016, the FASB issued Accounting Standards Update (ASU) 2016-01 which addresses certain aspects of recognition, measurement, presentation and disclosure of financial instruments. A financial instrument is defined as cash, evidence of ownership interest in a company or other entity, or a contract that both: (i) imposes on one entity a contractual obligation either to deliver cash or another financial instrument to a second entity or to exchange other financial instruments on potentially unfavorable terms with the second entity and (ii) conveys to that second entity a contractual right either to receive cash or another financial instruments from the first entity or to exchange other financial instruments on potentially favorable terms with the first entity. This pronouncement is effective for financial statements issued for annual periods beginning after December 15, 2017 and interim periods within those annual periods with earlier application permitted as of the beginning of the fiscal year of adoption. The Company is evaluating the impact that this new guidance will have on the Company’s Consolidated Financial Statements. 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 ACCOUN18

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)	9 Months Ended
	Sep. 30, 2017
Allowance for Doubtful Accounts Included in Accounts Receivable Net	The Allowance for Doubtful Accounts as of September 30, 2017, September 30, 2016 and December 31, 2016, which is included in Accounts Receivable, net on the accompanying unaudited consolidated balance sheets, was as follows: ($ millions) September 30, December 31, 2017 2016 2016 Allowance for Doubtful Accounts $ 1.5 $ 1.2 $ 1.1
Components of Accrued Revenue	The following table shows the components of Accrued Revenue as of September 30, 2017, September 30, 2016 and December 31, 2016. September 30, December 31, Accrued Revenue ($ millions) 2017 2016 2016 Regulatory Assets – Current $ 31.3 $ 28.0 $ 37.9 Unbilled Revenues 7.9 7.5 11.6 Total Accrued Revenue $ 39.2 $ 35.5 $ 49.5
Components of Exchange Gas Receivable	The following table shows the components of Exchange Gas Receivable as of September 30, 2017, September 30, 2016 and December 31, 2016. September 30, December 31, Exchange Gas Receivable ($ millions) 2017 2016 2016 Northern Utilities $ 8.9 $ 9.3 $ 7.8 Fitchburg 0.6 0.5 0.5 Total Exchange Gas Receivable $ 9.5 $ 9.8 $ 8.3
Components of Gas Inventory	The following table shows the components of Gas Inventory as of September 30, 2017, September 30, 2016 and December 31, 2016. September 30, December 31, Gas Inventory ($ millions) 2017 2016 2016 Natural Gas $ 0.4 $ 0.3 $ 0.3 Propane 0.2 0.2 0.2 Liquefied Natural Gas & Other 0.1 0.1 0.1 Total Gas Inventory $ 0.7 $ 0.6 $ 0.6
Regulatory Assets	September 30, December 31, Regulatory Assets consist of the following ($ millions) 2017 2016 2016 Retirement Benefits $ 76.2 $ 64.6 $ 75.9 Energy Supply & Other Rate Adjustment Mechanisms 28.2 23.2 32.7 Deferred Storm Charges 6.8 11.0 9.6 Environmental 9.9 12.2 10.8 Income Taxes 6.7 7.7 7.3 Other 5.5 5.8 5.7 Total Regulatory Assets $ 133.3 $ 124.5 $ 142.0 Less: Current Portion of Regulatory Assets (1) 31.3 28.0 37.9 Regulatory Assets – noncurrent $ 102.0 $ 96.5 $ 104.1 (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) 2017 2016 2016 Rate Adjustment Mechanisms $ 11.6 $ 8.5 $ 6.2 Gas Pipeline Refund (Note 6) 3.4 8.4 6.8 Total Regulatory Liabilities 15.0 16.9 13.0 Less: Current Portion of Regulatory Liabilities 15.0 13.2 10.4 Regulatory Liabilities – noncurrent $ — $ 3.7 $ 2.6
Fair Value of Marketable Securities	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) 2017 2016 2016 Equity Funds $ 1.9 $ 1.1 $ 1.1 Fixed Income Funds 1.5 0.8 0.8 Total Marketable Securities $ 3.4 $ 1.9 $ 1.9
Components of Energy Supply Obligations	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) 2017 2016 2016 Current: Exchange Gas Obligation $ 8.9 $ 9.3 $ 7.8 Renewable Energy Portfolio Standards 3.7 3.6 3.9 Power Supply Contract Divestitures 0.3 0.3 0.3 Total Energy Supply Obligations – Current 12.9 13.2 12.0 Noncurrent: Power Supply Contract Divestitures 1.0 1.4 1.3 Total Energy Supply Obligations $ 13.9 $ 14.6 $ 13.3

DIVIDENDS DECLARED PER SHARE (T

DIVIDENDS DECLARED PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2017
Schedule of Dividends Declared	Declaration Date Date Paid (Payable) Shareholder of Record Date Dividend Amount 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 10/19/16 11/28/16 11/14/16 $0.355 07/20/16 08/26/16 08/12/16 $0.355 04/20/16 05/27/16 05/13/16 $ 0.355 01/27/16 02/26/16 02/12/16 $ 0.355

SEGMENT INFORMATION (Tables)

SEGMENT INFORMATION (Tables)	9 Months Ended
	Sep. 30, 2017
Significant Segment Financial Data	The following table provides significant segment financial data for the three and nine months ended September 30, 2017 and September 30, 2016 and as of December 31, 2016 (millions): Gas Electric Non- Regulated Other Total 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 Three Months Ended September 30, 2016 Revenues $ 22.1 $ 55.2 $ 1.5 $ — $ 78.8 Segment Profit (Loss) (2.2 ) 5.3 0.3 0.1 3.5 Capital Expenditures 22.9 8.8 — 3.1 34.8 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 Nine Months Ended September 30, 2016 Revenues $ 124.1 $ 150.4 $ 4.6 $ — $ 279.1 Segment Profit 7.2 8.7 0.9 0.1 16.9 Capital Expenditures 44.8 21.8 — 7.8 74.4 Segment Assets 610.3 425.4 7.2 29.5 1,072.4 As of December 31, 2016 Segment Assets $ 645.2 $ 441.1 $ 6.8 $ 35.1 $ 1,128.2

DEBT AND FINANCING ARRANGEMEN21

DEBT AND FINANCING ARRANGEMENTS (Tables)	9 Months Ended
	Sep. 30, 2017
Details on Long Term Debt	Details on long-term debt at September 30, 2017, September 30, 2016 and December 31, 2016 are shown below: ($ millions) September 30, December 31, 2017 2016 2016 Unitil Corporation Senior Notes: 6.33% Notes, Due May 1, 2022 $ 20.0 $ 20.0 $ 20.0 3.70% Notes, Due August 1, 2026 30.0 30.0 30.0 Unitil Energy Systems, Inc.: First Mortgage Bonds: 5.24% Series, Due March 2, 2020 15.0 15.0 15.0 8.49% Series, Due October 14, 2024 9.0 12.0 9.0 6.96% Series, Due September 1, 2028 20.0 20.0 20.0 8.00% Series, Due May 1, 2031 15.0 15.0 15.0 6.32% Series, Due September 15, 2036 15.0 15.0 15.0 Fitchburg Gas and Electric Light Company: Long-Term Notes: 6.75% Notes, Due November 30, 2023 9.5 11.4 9.5 6.79% Notes, Due October 15, 2025 10.0 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 Northern Utilities Senior Notes: 6.95% Senior Notes, Series A, Due December 3, 2018 20.0 30.0 20.0 5.29% Senior Notes, Due March 2, 2020 25.0 25.0 25.0 7.72% Senior Notes, Series B, Due December 3, 2038 50.0 50.0 50.0 4.42% Senior Notes, Due October 15, 2044 50.0 50.0 50.0 Granite State Senior Notes: 7.15% Senior Notes, Due December 15, 2018 6.7 10.0 6.7 Unitil Realty Corp.: Senior Secured Notes: 8.00% Notes, Due Through August 1, 2017 — 0.6 0.4 Total Long-Term Debt 336.2 355.0 336.6 Less: Unamortized Debt Issuance Costs 2.8 3.0 3.0 Total Long-Term Debt, net of Unamortized Debt Issuance Costs 333.4 352.0 333.6 Less: Current Portion 29.8 17.0 16.8 Total Long-term Debt, Less Current Portion $ 303.6 $ 335.0 $ 316.8
Fair Value of Long Term Debt	($ millions) September 30, December 31, 2017 2016 2016 Estimated Fair Value of Long-Term Debt $ 383.0 $ 405.8 $ 370.3
Borrowing Limits Amounts Outstanding and Amounts Available under Revolving Credit Facility	The following table details the borrowing limits, amounts outstanding and amounts available under the revolving Credit Facility as of September 30, 2017, September 30, 2016 and December 31, 2016: Revolving Credit Facility ($ millions) September 30, December 31, 2017 2016 2016 Limit $ 120.0 $ 120.0 $ 120.0 Short-Term Borrowings Outstanding $ 111.9 $ 36.9 $ 81.9 Letters of Credit Outstanding $ 1.1 $ 1.1 $ 1.1 Available $ 7.0 $ 82.0 $ 37.0

COMMON STOCK AND PREFERRED ST22

COMMON STOCK AND PREFERRED STOCK (Tables)	9 Months Ended
	Sep. 30, 2017
Restricted Stock Units Issued	The equity portion of Restricted Stock Units activity during the nine months ended September 30, 2017 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, 2016 43,345 $ 33.40 Restricted Stock Units Granted — — Dividend Equivalents Earned 998 $ 47.32 Restricted Stock Units Settled — — Restricted Stock Units as of September 30, 2017 44,343 $ 33.72

ENVIRONMENTAL MATTERS (Tables)

ENVIRONMENTAL MATTERS (Tables)	9 Months Ended
	Sep. 30, 2017
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, 2017 and 2016. Environmental Obligations ($ millions) Fitchburg Northern Total Nine months ended September 30, 2017 2016 2017 2016 2017 2016 Total Balance at Beginning of Period $ 0.1 $ 1.2 $ 1.8 $ 1.6 $ 1.9 $ 2.8 Additions — — 0.5 0.9 0.5 0.9 Less: Payments / Reductions — 0.1 0.2 0.6 0.2 0.7 Total Balance at End of Period 0.1 1.1 2.1 1.9 2.2 3.0 Less: Current Portion 0.1 0.1 0.4 0.2 0.5 0.3 Noncurrent Balance at End of Period $ — $ 1.0 $ 1.7 $ 1.7 $ 1.7 $ 2.7

RETIREMENT BENEFIT OBLIGATIONS

RETIREMENT BENEFIT OBLIGATIONS (Tables)	9 Months Ended
	Sep. 30, 2017
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: 2017 2016 Used to Determine Plan Costs Discount Rate 4.10 % 4.30 % Rate of Compensation Increase 3.00 % 3.00 % Expected Long-term rate of return on plan assets 7.75 % 8.00 % Health Care Cost Trend Rate Assumed for Next Year 8.00 % 7.00 % Ultimate Health Care Cost Trend Rate 4.00 % 4.00 % Year that Ultimate Health Care Cost Trend Rate is reached 2025 2022
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, 2017 2016 2017 2016 2017 2016 Service Cost $ 824 $ 851 $ 744 $ 652 $ 115 $ 41 Interest Cost 1,514 1,486 978 808 98 96 Expected Return on Plan Assets (1,826 ) (1,814 ) (337 ) (301 ) — — Prior Service Cost Amortization 66 66 350 372 47 47 Actuarial Loss Amortization 1,165 1,099 524 262 74 94 Sub-total 1,743 1,688 2,259 1,793 334 278 Amounts Capitalized and Deferred (932 ) (839 ) (1,226 ) (904 ) — — Net Periodic Benefit Cost Recognized $ 811 $ 849 $ 1,033 $ 889 $ 334 $ 278 Pension Plan PBOP Plan SERP Nine Months Ended September 30, 2017 2016 2017 2016 2017 2016 Service Cost $ 2,471 $ 2,553 $ 2,231 $ 1,956 $ 345 $ 123 Interest Cost 4,543 4,458 2,935 2,424 294 288 Expected Return on Plan Assets (5,479 ) (5,442 ) (1,010 ) (903 ) — — Prior Service Cost Amortization 197 198 1,049 1,116 141 141 Actuarial Loss Amortization 3,496 3,297 1,573 786 222 282 Sub-total 5,228 5,064 6,778 5,379 1,002 834 Amounts Capitalized and Deferred (2,402 ) (2,246 ) (3,418 ) (2,508 ) — — Net Periodic Benefit Cost Recognized $ 2,826 $ 2,818 $ 3,360 $ 2,871 $ 1,002 $ 834

Summary of Significant Accoun25

Summary of Significant Accounting Policies - Additional Information (Detail) Bcf in Billions	9 Months Ended
	Sep. 30, 2017USD ($)SubsidiarymiBcf	Dec. 31, 2016USD ($)Bcf	Sep. 30, 2016USD ($)Bcf
Significant Accounting Policies [Line Items]
Length Of Pipeline | mi	86
Cost of removal obligation	$ 84,800,000	$ 77,000,000	$ 77,400,000
Regulatory Assets	$ 133,300,000	$ 142,000,000	$ 124,500,000
Number of Natural Gas Storage Outstanding | Bcf	1.2	2	2.9
Investments in trading securities	$ 3,400,000	$ 1,900,000	$ 1,900,000
Not Designated as Hedging Instruments
Significant Accounting Policies [Line Items]
Derivative Assets, not designated as hedging instruments	$ 100,000	400,000	200,000
Maximum
Significant Accounting Policies [Line Items]
Cash equivalents maturity period	3 months
ISO-NE Obligations
Significant Accounting Policies [Line Items]
Cash Deposits	$ 4,800,000	2,800,000	3,500,000
Natural Gas Hedging Program
Significant Accounting Policies [Line Items]
Cash Deposits	0	0	0
Deferred Storm Charges
Significant Accounting Policies [Line Items]
Regulatory Assets	6,800,000	$ 9,600,000	$ 11,000,000
Deferred Storm Charges | Recovered over Next Year
Significant Accounting Policies [Line Items]
Regulatory Assets	1,400,000
Environmental and Rate Case Costs and Other Expenditures | Recovered over the next seven years
Significant Accounting Policies [Line Items]
Regulatory Assets	$ 7,400,000
Unitil Service; Unitil Realty; and Unitil Resources
Significant Accounting Policies [Line Items]
Number of Subsidiaries | Subsidiary	3
Utilities
Significant Accounting Policies [Line Items]
Number of Subsidiaries | Subsidiary	3

Allowance for Doubtful Accounts

Allowance for Doubtful Accounts Included in Accounts Receivable Net (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Valuation Allowance [Line Items]
Allowance for Doubtful Accounts	$ 1.5	$ 1.1	$ 1.2

Components of Accrued Revenue (

Components of Accrued Revenue (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Deferred Revenue Arrangement [Line Items]
Accrued Revenue	$ 39.2	$ 49.5	$ 35.5
Unbilled Revenues
Deferred Revenue Arrangement [Line Items]
Accrued Revenue	7.9	11.6	7.5
Regulatory Assets
Deferred Revenue Arrangement [Line Items]
Accrued Revenue	$ 31.3	$ 37.9	$ 28

Components of Exchange Gas Rece

Components of Exchange Gas Receivable (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Receivables [Line Items]
Total Exchange Gas Receivable	$ 9.5	$ 8.3	$ 9.8
Northern Utilities Inc
Receivables [Line Items]
Total Exchange Gas Receivable	8.9	7.8	9.3
Fitchburg Gas and Electric Light Company
Receivables [Line Items]
Total Exchange Gas Receivable	$ 0.6	$ 0.5	$ 0.5

Components of Gas Inventory (De

Components of Gas Inventory (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 0.7	$ 0.6	$ 0.6
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	0.3	0.3
Propane
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 0.2	$ 0.2	$ 0.2

Regulatory Assets (Detail)

Regulatory Assets (Detail) - USD ($) $ in Millions		Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Regulatory Assets [Line Items]
Regulatory Assets		$ 133.3	$ 142	$ 124.5
Less: Current Portion of Regulatory Assets	[1]	31.3	37.9	28
Regulatory Assets - noncurrent		102	104.1	96.5
Environmental Matters
Regulatory Assets [Line Items]
Regulatory Assets		9.9	10.8	12.2
Other Assets
Regulatory Assets [Line Items]
Regulatory Assets		5.5	5.7	5.8
Retirement Benefits
Regulatory Assets [Line Items]
Regulatory Assets		76.2	75.9	64.6
Deferred Storm Charges
Regulatory Assets [Line Items]
Regulatory Assets		6.8	9.6	11
Income Taxes
Regulatory Assets [Line Items]
Regulatory Assets		6.7	7.3	7.7
Energy Supply & Other Rate Adjustment Mechanisms
Regulatory Assets [Line Items]
Regulatory Assets		$ 28.2	$ 32.7	$ 23.2
[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, 2017	Dec. 31, 2016	Sep. 30, 2016
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 15	$ 13	$ 16.9
Less: Current Portion of Regulatory Liabilities	15	10.4	13.2
Regulatory Liabilities - noncurrent		2.6	3.7
Rate Adjustment Mechanisms
Regulatory Liabilities [Line Items]
Regulatory Liabilities	11.6	6.2	8.5
Gas Pipeline Refund
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 3.4	$ 6.8	$ 8.4

Fair Value of Marketable Securi

Fair Value of Marketable Securities (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Trading Securities	$ 3.4	$ 1.9	$ 1.9
Fair Value, Inputs, Level 1
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Trading Securities	3.4	1.9	1.9
Fair Value, Inputs, Level 1 | Equity Funds
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Trading Securities	1.9	1.1	1.1
Fair Value, Inputs, Level 1 | Fixed Income Funds
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Trading Securities	$ 1.5	$ 0.8	$ 0.8

Components of Energy Supply Obl

Components of Energy Supply Obligations (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Contractual Obligation [Line Items]
Energy Supply Obligations - Current	$ 12.9	$ 12	$ 13.2
Power Supply Contract Divestitures, Noncurrent	1	1.3	1.4
Total Energy Supply Obligations	13.9	13.3	14.6
Exchange Gas Obligation
Contractual Obligation [Line Items]
Energy Supply Obligations - Current	8.9	7.8	9.3
Renewable Energy Portfolio Standards
Contractual Obligation [Line Items]
Energy Supply Obligations - Current	3.7	3.9	3.6
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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Dividends Payable [Line Items]
Dividend Amount	$ 0.360	$ 0.355	$ 1.080	$ 1.065
Group One
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 Two
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 Three
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 Four
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
Group Five
Dividends Payable [Line Items]
Declaration Date			Oct. 19, 2016
Date Paid (Payable)			Nov. 28, 2016
Shareholder of Record Date			Nov. 14, 2016
Dividend Amount			$ 0.355
Group Six
Dividends Payable [Line Items]
Declaration Date			Jul. 20, 2016
Date Paid (Payable)			Aug. 26, 2016
Shareholder of Record Date			Aug. 12, 2016
Dividend Amount			$ 0.355
Group Seven
Dividends Payable [Line Items]
Declaration Date			Apr. 20, 2016
Date Paid (Payable)			May 27, 2016
Shareholder of Record Date			May 13, 2016
Dividend Amount			$ 0.355
Group Eight
Dividends Payable [Line Items]
Declaration Date			Jan. 27, 2016
Date Paid (Payable)			Feb. 26, 2016
Shareholder of Record Date			Feb. 12, 2016
Dividend Amount			$ 0.355

Significant Segment Financial D

Significant Segment Financial Data (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	$ 84	$ 78.8	$ 290.8	$ 279.1
Segment Profit (Loss)	2.3	3.5	17.8	16.9
Capital Expenditures	39.3	34.8	84.2	74.4
Segment Assets	1,179.9	1,072.4	1,179.9	1,072.4	$ 1,128.2
Gas Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	25.1	22.1	131.9	124.1
Segment Profit (Loss)	(2.1)	(2.2)	7.9	7.2
Capital Expenditures	26	22.9	48.7	44.8
Segment Assets	661.2	610.3	661.2	610.3	645.2
Electric
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	57.5	55.2	154.4	150.4
Segment Profit (Loss)	4.1	5.3	9.3	8.7
Capital Expenditures	10	8.8	23.8	21.8
Segment Assets	461.2	425.4	461.2	425.4	441.1
All Other Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Segment Profit (Loss)		0.1	(0.2)	0.1
Capital Expenditures	3.3	3.1	11.7	7.8
Segment Assets	50.2	29.5	50.2	29.5	35.1
Unregulated Operation
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Revenues	1.4	1.5	4.5	4.6
Segment Profit (Loss)	0.3	0.3	0.8	0.9
Segment Assets	$ 7.3	$ 7.2	$ 7.3	$ 7.2	$ 6.8

Details on Long Term Debt (Deta

Details on Long Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Total Long-Term Debt	$ 336.2	$ 336.6	$ 355
Less: Unamortized Debt Issuance Costs	2.8	3	3
Long-Term Debt	333.4	333.6	352
Less: Current Portion	29.8	16.8	17
Total Long-Term Debt, Less Current Portion	303.6	316.8	335
Long-Term Debt	333.4	333.6	352
6.33% Notes, Due May 1, 2022
Debt Instrument [Line Items]
Total Long-Term Debt	20	20	20
3.70% Senior Unsecured 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% Series, Due March 2, 2020
Debt Instrument [Line Items]
Total Long-Term Debt	15	15	15
Unitil Energy Systems Inc | First Mortgage Bonds 8.49% Series, Due October 14, 2024
Debt Instrument [Line Items]
Total Long-Term Debt	9	9	12
Unitil Energy Systems Inc | First Mortgage Bonds 6.96% Series, Due September 1, 2028
Debt Instrument [Line Items]
Total Long-Term Debt	20	20	20
Unitil Energy Systems Inc | First Mortgage Bonds 8.00% Series, Due May 1, 2031
Debt Instrument [Line Items]
Total Long-Term Debt	15	15	15
Unitil Energy Systems Inc | First Mortgage Bonds 6.32% Series, Due September 15, 2036
Debt Instrument [Line Items]
Total Long-Term Debt	15	15	15
Fitchburg Gas and Electric Light Company | 6.75% Notes, Due November 30, 2023
Debt Instrument [Line Items]
Total Long-Term Debt	9.5	9.5	11.4
Fitchburg Gas and Electric Light Company | 6.79% Notes, Due October 15, 2025
Debt Instrument [Line Items]
Total Long-Term Debt	10	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
Northern Utilities Inc | 6.95% Senior Notes, Series A, Due December 3, 2018
Debt Instrument [Line Items]
Total Long-Term Debt	20	20	30
Northern Utilities Inc | 5.29% Senior Notes, Due March 2, 2020
Debt Instrument [Line Items]
Total Long-Term Debt	25	25	25
Northern Utilities Inc | 7.72% Senior Notes, Series B, 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	$ 6.7	6.7	10
Unitil Realty Corp | 8.00% Senior Secured Notes, Due August 1, 2017
Debt Instrument [Line Items]
Total Long-Term Debt		$ 0.4	$ 0.6

Details on Long Term Debt (Pare

Details on Long Term Debt (Parenthetical) (Detail)	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
6.33% 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 Unsecured 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% Series, 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% Series, 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% Series, 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% Series, 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% Series, 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% 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% 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
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
6.95% Senior Notes, Series A, 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, Series B, 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
8.00% Senior Secured Notes, Due August 1, 2017 | Unitil Realty Corp
Debt Instrument [Line Items]
Stated interest rate		8.00%	8.00%
Debt instrument due date		Aug. 1, 2017	Aug. 1, 2017

Estimated Fair Value of Long Te

Estimated Fair Value of Long Term Debt (Detail) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Fair Value, Inputs, Level 2
Debt Instrument [Line Items]
Estimated Fair Value of Long-Term Debt	$ 383	$ 370.3	$ 405.8

Debt and Financing Arrangemen39

Debt and Financing Arrangements - Additional Information (Detail) - USD ($)	Jul. 14, 2017	Oct. 04, 2013	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Oct. 30, 2015
Line of Credit Facility [Line Items]
Weighted average interest rate on short term borrowings			2.30%	1.80%	1.70%
Deferred financing cost			$ 100,000
Capital lease obligation, current			3,100,000	$ 3,000,000	$ 3,100,000
Capital lease obligation, noncurrent			6,400,000	8,300,000	9,000,000
Accounts Payable			24,100,000	32,400,000	23,100,000
Guarantee outstanding			$ 19,800,000
Unitil Service Corp.
Line of Credit Facility [Line Items]
Capital lease obligation, total capitalized cost						$ 13,400,000
Capital lease obligation, maturity period			Oct. 30, 2015
Capital lease obligation, current			$ 2,700,000
Capital lease obligation, noncurrent			5,800,000
Northern Utilities Inc
Line of Credit Facility [Line Items]
Natural gas storage inventory			9,000,000	9,900,000	9,300,000
Accounts Payable			100,000	2,100,000	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			164,200,000
Repayments of lines of credit			$ 134,200,000
3.52% Senior Unsecured Notes, Due 2027 | Northern Utilities Inc
Line of Credit Facility [Line Items]
Senior Notes	$ 20,000,000
Debt instrument due date, year	2,027
Stated interest rate	3.52%
3.52% Senior Unsecured Notes, Due 2027 | Fitchburg Gas and Electric Light Company
Line of Credit Facility [Line Items]
Senior Notes	$ 10,000,000
Debt instrument due date, year	2,027
Stated interest rate	3.52%
4.32% Senior Unsecured Notes, Due 2047 | Northern Utilities Inc
Line of Credit Facility [Line Items]
Senior Notes	$ 30,000,000
Debt instrument due date, year	2,047
Stated interest rate	4.32%
4.32% Senior Unsecured Notes, Due 2047 | Fitchburg Gas and Electric Light Company
Line of Credit Facility [Line Items]
Senior Notes	$ 15,000,000
Debt instrument due date, year	2,047
Stated interest rate	4.32%
3.72% Senior Unsecured Notes, Due 2027 | Granite State Gas Transmission Inc
Line of Credit Facility [Line Items]
Senior Notes	$ 15,000,000
Debt instrument due date, year	2,027
Stated interest rate	3.72%
Credit Facility | Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility		$ 120,000,000
Sublimit for the issuance of standby letters of credit		25,000,000
Credit Facility by an aggregate additional amount		$ 30,000,000
Revolving credit facility termination date		Oct. 4, 2020
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, 2017, September 30, 2016 and December 31, 2016, the Company was in compliance with the covenants contained in the Credit Facility in effect on that date.
Credit Facility | Revolving Credit Facility | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Line Items]
Credit facility, daily fluctuating rate of interest		1.25%
Senior Unsecured Notes | Private Placement
Line of Credit Facility [Line Items]
Senior Notes	$ 90,000,000
7.15% Senior Notes, Due December 15, 2018 | Granite State Gas Transmission Inc
Line of Credit Facility [Line Items]
Senior Notes			$ 6,700,000
Stated interest rate			7.15%	7.15%	7.15%

Borrowing Limits Amounts Outsta

Borrowing Limits Amounts Outstanding and Amounts Available under Revolving Credit Facility (Detail) - USD ($)	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Debt Instrument [Line Items]
Short-Term Borrowings Outstanding	$ 111,900,000	$ 81,900,000	$ 36,900,000
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, limit	120,000,000	120,000,000	120,000,000
Short-Term Borrowings Outstanding	111,900,000	81,900,000	36,900,000
Letters of Credit Outstanding	1,100,000	1,100,000	1,100,000
Available revolving credit facility	$ 7,000,000	$ 37,000,000	$ 82,000,000

Common Stock and Preferred St41

Common Stock and Preferred Stock - Additional Information (Detail) - USD ($)	Oct. 02, 2017	Jan. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Class of Stock [Line Items]
Common stock, shares outstanding			14,119,893	14,060,147	14,119,893	14,060,147	14,065,230
Common stock, shares issued					20,564	24,697
Proceeds from Issuance of Common Stock					$ 1,000,000	$ 1,000,000
Share based compensation expense					$ 2,600,000	2,000,000
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			$ 900,000	$ 600,000	$ 900,000	600,000	$ 800,000
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					$ 967,000
Dividend and Distribution Reinvestment and Share Purchase Plan | Average
Class of Stock [Line Items]
Common stock price per share			$ 47.02		$ 47.02
Dividend and Distribution Reinvestment and Share Purchase Plan | Common Stock
Class of Stock [Line Items]
Common stock, shares issued					20,564
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			89,326	95,506	89,326	95,506
Restricted stock weighted average grant date fair value					$ 39.54	$ 35.30
Unrecognized share based compensation			$ 1,000,000		$ 1,000,000
Share compensation recognition period					2 years 4 months 24 days
Forfeitures under the stock plan					831
Cancellations under the stock plan					0
Restricted Stock Units Granted		34,930
Aggregate Market Value		$ 1,600,000
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					0
Restricted stock units outstanding				34,498		34,498
Weighted-Average Stock Price				$ 32.03		$ 32.03
Restricted Stock Units (RSUs) | Subsequent Event
Class of Stock [Line Items]
Restricted Stock Units Granted	10,746

Restricted Stock Units Issued (

Restricted Stock Units Issued (Detail) - Restricted Stock Units (RSUs)	9 Months Ended
	Sep. 30, 2017$ / sharesshares
Restricted Stock Units
Beginning Restricted Stock Units | shares	43,345
Restricted Stock Units Granted | shares	0
Dividend Equivalents Earned | shares	998
Restricted Stock Units Settled | shares	0
Ending Restricted Stock Units | shares	44,343
Weighted-Average Stock Price
Beginning Restricted Stock Units | $ / shares	$ 33.40
Restricted Stock Units Granted | $ / shares	0
Dividend Equivalents Earned | $ / shares	47.32
Restricted Stock Units Settled | $ / shares	0
Ending Restricted Stock Units | $ / shares	$ 33.72

Regulatory Matters - Additional

Regulatory Matters - Additional Information (Detail) $ in Millions

Aug. 18, 2017USD ($)

Aug. 01, 2017USD ($)

Jun. 21, 2017USD ($)

Jun. 05, 2017USD ($)

May 31, 2017USD ($)

Apr. 25, 2017USD ($)

Apr. 20, 2017USD ($)

Oct. 31, 2016USD ($)

Aug. 19, 2016MW

Apr. 29, 2016USD ($)

Apr. 15, 2015USD ($)

Sep. 30, 2017USD ($)StateCustomer

Dec. 31, 2015USD ($)

Jun. 30, 2027MW

Dec. 31, 2022MWh

Aug. 25, 2017MW

Jun. 30, 2017MW

Jun. 23, 2017kW

Apr. 28, 2017

Dec. 31, 2016USD ($)

Sep. 30, 2016USD ($)

Regulatory Assets [Line Items]

Current Portion of Regulatory Liabilities

$ 15

$ 10.4

$ 13.2

Power capacity facility for small customers | kW

100

Northern Utilities Inc

Regulatory Assets [Line Items]

Increase in annual revenue

$ 0.7

$ 6

Amendment effective date

May 1, 2017

Annual TIRA Adjustment

$ 1.1

TIRA initial term

Four years

Pipeline refund received

$ 22

Current Portion of Regulatory Liabilities

$ 3.4

Northern Utilities Inc | Maine

Regulatory Assets [Line Items]

Number of new customers | Customer

1,000

Potential regulated operating revenue

$ 1

Construction completion period

3 years

Grace period to receive refund

3 years

Northern Utilities Inc | Maine | Second TAB program

Regulatory Assets [Line Items]

Number of new customers | Customer

2,000

Potential regulated operating revenue

$ 2

Northern Utilities Inc | New Hampshire

Regulatory Assets [Line Items]

Increase in annual revenue

$ 1.6

Amendment effective date

Jul. 31, 2017

Deferred cost

$ 0.3

Grace period to receive refund

3 years

Northern Utilities Inc | New Hampshire | Natural Gas Distribution

Regulatory Assets [Line Items]

Increase in annual revenue

$ 4.7

Granite State Gas Transmission Inc | Gas Transportation and Storage

Regulatory Assets [Line Items]

Increase in annual revenue

$ 0.2

Amendment effective date

Aug. 1, 2017

Jul. 28, 2017

Unitil Energy Systems Inc | New Hampshire

Regulatory Assets [Line Items]

Permanent rate increase

$ 4.1

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

Regulatory Assets [Line Items]

Permanent rate increase

$ 0.9

Fitchburg Gas and Electric Light Company

Regulatory Assets [Line Items]

Increase in annual revenue

$ 0.5

Recovery amount

0.9

Percentage of waiver approved on annual changes in the revenue requirement eligible for recovery

1.50%

Revenues sought approval to collect, deferred for recovery in future periods

$ 0.4

Percentage of waiver sought on annual changes in the revenue requirement eligible for recovery

1.50%

Number of states with electric distribution companies | State

3

Fitchburg Gas and Electric Light Company | Solar Generation

Regulatory Assets [Line Items]

Power generation capacity | MW

1.3

Expected completion date of facility

2017-11

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

Regulatory Assets [Line Items]

Power generation capacity | MW

400

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

9,450,000

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

Regulatory Assets [Line Items]

Power generation capacity | MW

1,600

Fitchburg Gas and Electric Light Company | Electric base

Regulatory Assets [Line Items]

Increase in annual revenue

$ 2.1

Amendment effective date

May 1, 2016

Annual revenue adjustment

$ 0.5

Fitchburg Gas and Electric Light Company | Gas base

Regulatory Assets [Line Items]

Increase in annual revenue

$ 1.6

Amendment effective date

May 1, 2016

Environmental Matters - Additio

Environmental Matters - Additional Information (Detail) - Environmental Restoration Costs	9 Months Ended
	Sep. 30, 2017
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, 2017	Sep. 30, 2016	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016
Environmental Exit Cost [Line Items]
Total Balance at Beginning of period	$ 1.9	$ 2.8
Additions	0.5	0.9
Less: Payments / Reductions	0.2	0.7
Total Balance at End of period	2.2	3
Less: Current Portion			$ 0.5	$ 0.4	$ 0.3
Noncurrent Balance			1.7	1.5	2.7
Total Balance at End of period	2.2	3	2.2	1.9	3
Fitchburg Gas and Electric Light Company
Environmental Exit Cost [Line Items]
Total Balance at Beginning of period	0.1	1.2
Less: Payments / Reductions		0.1
Total Balance at End of period	0.1	1.1
Less: Current Portion			0.1		0.1
Noncurrent Balance					1
Total Balance at End of period	0.1	1.1	0.1	0.1	1.1
Northern Utilities Inc
Environmental Exit Cost [Line Items]
Total Balance at Beginning of period	1.8	1.6
Additions	0.5	0.9
Less: Payments / Reductions	0.2	0.6
Total Balance at End of period	2.1	1.9
Less: Current Portion			0.4		0.2
Noncurrent Balance			1.7		1.7
Total Balance at End of period	$ 2.1	$ 1.9	$ 2.1	$ 1.8	$ 1.9

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) $ in Millions	9 Months Ended
	Sep. 30, 2017USD ($)
Income Taxes [Line Items]
Net Operating Loss Carryforwards	$ 23.9
NOL carryforward assets expiration date	2,029
Alternative minimum tax credit carryforwards	$ 3.4
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, 2014; December 31, 2015; and December 31, 2016. The Company received notice that its Maine income tax return filings for the years ended December 31, 2014; December 31, 2015; and December 31, 2016 are under examination by the Maine Revenue Service. Auditor fieldwork is scheduled to occur in the fourth quarter of 2017 and the Company does not expect that the results of this examination will have a material impact on its financial position, operating results or cash flows.

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, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	4.10%	4.30%
Rate of Compensation Increase	3.00%	3.00%
Expected Long-term rate of return on plan assets	7.75%	8.00%
Health Care Cost Trend Rate Assumed for Next Year	8.00%	7.00%
Ultimate Health Care Cost Trend Rate	4.00%	4.00%
Year that Ultimate Health Care Cost Trend Rate is reached	2,025	2,022

Components of Retirement Plan C

Components of Retirement Plan Costs (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 824	$ 851	$ 2,471	$ 2,553
Interest Cost	1,514	1,486	4,543	4,458
Expected Return on Plan Assets	(1,826)	(1,814)	(5,479)	(5,442)
Prior Service Cost Amortization	66	66	197	198
Actuarial Loss Amortization	1,165	1,099	3,496	3,297
Sub-total	1,743	1,688	5,228	5,064
Amounts Capitalized and Deferred	(932)	(839)	(2,402)	(2,246)
Net Periodic Benefit Cost Recognized	811	849	2,826	2,818
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service Cost	744	652	2,231	1,956
Interest Cost	978	808	2,935	2,424
Expected Return on Plan Assets	(337)	(301)	(1,010)	(903)
Prior Service Cost Amortization	350	372	1,049	1,116
Actuarial Loss Amortization	524	262	1,573	786
Sub-total	2,259	1,793	6,778	5,379
Amounts Capitalized and Deferred	(1,226)	(904)	(3,418)	(2,508)
Net Periodic Benefit Cost Recognized	1,033	889	3,360	2,871
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service Cost	115	41	345	123
Interest Cost	98	96	294	288
Prior Service Cost Amortization	47	47	141	141
Actuarial Loss Amortization	74	94	222	282
Sub-total	334	278	1,002	834
Net Periodic Benefit Cost Recognized	$ 334	$ 278	$ 1,002	$ 834

Retirement Benefit Obligation49

Retirement Benefit Obligations - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2017USD ($)
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions to benefit plan	$ 4,100,000
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Contributions to benefit plan	2,800,000
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Benefit payments under SERP Plan	25,600
Expected additional benefit payments under SERP Plan in 2016	$ 8,500