Unitil (UTL) 10-K 1 Feb 22 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Dec. 31, 2021	Jan. 28, 2022	Jun. 30, 2021
Document Information [Line Items]
Entity Interactive Data Current	Yes
Document Transition Report	false
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Entity Registrant Name	UNITIL CORPORATION
Entity Central Index Key	0000755001
Entity File Number	1-8858
Entity Tax Identification Number	02-0381573
Entity Incorporation, State or Country Code	NH
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Address, Address Line One	6 Liberty Lane West
Entity Address, City or Town	Hampton
Entity Address, Postal Zip Code	03842-1720
Entity Address, State or Province	NH
City Area Code	603
Local Phone Number	772-0775
Trading Symbol	UTL
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		15,978,791
Title of 12(b) Security	Common Stock
Document Annual Report	true
Entity Public Float			$ 785,923,009
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
ICFR Auditor Attestation Flag	true
Auditor Name	Deloitte & Touche LLP
Auditor Firm ID	34
Auditor Location	Boston, MA

CONSOLIDATED STATEMENTS OF EARN

CONSOLIDATED STATEMENTS OF EARNINGS - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Revenues
Total Operating Revenues	$ 473.3	$ 418.6	$ 438.2
Operating Expenses
Operation and Maintenance	68.7	65.7	67.2
Depreciation and Amortization	59.5	54.5	52
Taxes Other Than Income Taxes	24.5	23.9	22.7
Total Operating Expenses	395.5	347.2	365.1
Operating Income	77.8	71.4	73.1
Interest Expense, Net	25.6	23.8	23.7
Other Expense (Income), Net	4.6	5.2	(8.6)
Income Before Income Taxes	47.6	42.4	58
Provision for Income Taxes	11.5	10.2	13.8
Net Income Applicable to Common Shares	$ 36.1	$ 32.2	$ 44.2
Earnings per Common Share—Basic and Diluted	$ 2.35	$ 2.15	$ 2.97
Weighted Average Common Shares Outstanding—(Basic and Diluted)	15.4	15	14.9
Electric
Operating Revenues
Total Operating Revenues	$ 248.5	$ 227.2	$ 233.9
Operating Expenses
Total Operating Expenses	151.1	134.3	142
Gas
Operating Revenues
Total Operating Revenues	224.8	191.4	203.4
Other
Operating Revenues
Total Operating Revenues			0.9
Operating Expenses
Total Operating Expenses	$ 91.7	$ 68.8	$ 81.2

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Current Assets:
Cash and Cash Equivalents		$ 6.5	$ 6
Accounts Receivable, Net		66.9	62
Accrued Revenue		61.2	50.9
Exchange Gas Receivable		7.4	4.9
Gas Inventory		1	0.6
Materials and Supplies		8.6	8.5
Prepayments and Other		8.1	6.4
Total Current Assets		159.7	139.3
Utility Plant:
Electric		602.4	575.9
Gas		972.6	920.2
Common		66.4	64.1
Construction Work in Progress		47.5	34.8
Utility Plant		1,688.9	1,595
Less: Accumulated Depreciation		431.7	401.8
Net Utility Plant		1,257.2	1,193.2
Other Noncurrent Assets:
Regulatory Assets		108.9	127.4
Operating Lease Right of Use Assets		4.7	5.2
Other Assets		9.8	12.8
Total Other Noncurrent Assets		123.4	145.4
TOTAL ASSETS		1,540.3	1,477.9
Current Liabilities:
Accounts Payable		52.4	33.2
Short-Term Debt		64.1	54.7
Long-Term Debt, Current Portion	[1]	8.2	8.5
Regulatory Liabilities		9.5	5.5
Energy Supply Obligations		14.5	10.4
Environmental Obligations		0.5	0.3
Other Current Liabilities		24.3	23.5
Total Current Liabilities		173.5	136.1
Noncurrent Liabilities:
Retirement Benefit Obligations		133.9	162.3
Deferred Income Taxes, net		127.7	109
Cost of Removal Obligations		107.5	105.2
Regulatory Liabilities		42.6	44.3
Environmental Obligations		2.2	1.8
Other Noncurrent Liabilities		6.6	6.9
Total Noncurrent Liabilities		420.5	429.5
Capitalization:
Long-Term Debt, Less Current Portion		497.8	523.1
Stockholders' Equity:
Common Equity (Outstanding 15,977,766 and 15,012,310 Shares)		332.1	285.3
Retained Earnings		116.2	103.7
Total Common Stock Equity		448.3	389
Preferred Stock		0.2	0.2
Total Stockholders' Equity		448.5	389.2
Total Capitalization		946.3	912.3
Commitments and Contingencies (Note 7)
TOTAL LIABILITIES AND CAPITALIZATION		$ 1,540.3	$ 1,477.9
[1]	The Current Portion of Long-Term Debt includes sinking fund payments.

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - shares	Dec. 31, 2021	Dec. 31, 2020
Common Equity Outstanding	15,977,766	15,012,310

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Activities:
Net Income	$ 36.1	$ 32.2	$ 44.2
Adjustments to Reconcile Net Income to Cash Provided by Operating Activities:
Depreciation and Amortization	59.5	54.5	52
Deferred Tax Provision	10.8	9.3	13.5
Gain on Divestiture, net (See Note 1)			(13.4)
Changes in Working Capital Items:
Accounts Receivable	(4.9)	(6.9)	11.7
Accrued Revenue	(10.3)	(0.9)	4.7
Regulatory Liabilities	4	(1.9)	(4.1)
Exchange Gas Receivable	(2.5)	1.2	2
Accounts Payable	19.2	(4.4)	(5)
Other Changes in Working Capital Items	0.7	(2.4)	4.6
Deferred Regulatory and Other Charges	(2.7)	(9.3)	(5.3)
Other, net	(2.1)	4.3
Cash Provided by Operating Activities	107.8	75.7	104.9
Investing Activities:
Property, Plant and Equipment Additions	(115)	(122.6)	(119.2)
Proceeds from Divestiture, Net (See Note 1)			13.4
Cash Used In Investing Activities	(115)	(122.6)	(105.8)
Financing Activities:
Proceeds from (Repayment of) Short-Term Debt, net	9.4	(3.9)	(24.2)
Issuance of Long-Term Debt		99.7	70
Repayment of Long-Term Debt	(25.8)	(24.8)	(18.8)
Long-Term Debt Issuance Costs		(0.6)	(0.4)
Decrease in Capital Lease Obligations	(0.1)	(0.1)	(5.3)
Net Increase (Decrease) in Exchange Gas Financing	2.3	(1.1)	(2)
Dividends Paid	(23.6)	(22.6)	(22.1)
Proceeds from Issuance of Common Stock	45.5	1.1	1.1
Cash Provided by (Used In) Financing Activities	7.7	47.7	(1.7)
Net Increase (Decrease) in Cash and Cash Equivalents	0.5	0.8	(2.6)
Cash and Cash Equivalents at Beginning of Year	6	5.2	7.8
Cash and Cash Equivalents at End of Year	6.5	6	5.2
Supplemental Information:
Interest Paid	26	23.7	24.1
Income Taxes Paid	1.4	0.9	0.8
Payments on Capital Leases	0.2	0.3	5.5
Capital Expenditures Included in Accounts Payable	4.9	1.7	0.6
Right-of-Use Assets Obtained in Exchange for Lease Obligations	$ 0.7	$ 1.2	$ 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, 2018	$ 351.1	$ 279.1	$ 72
Net Income	44.2		44.2
Dividends on Common Shares	(22.1)		(22.1)
Shares Issued Under Stock Plans	2.3	2.3
Issuance of Common Shares	1.1	1.1
Ending Balance at Dec. 31, 2019	376.6	282.5	94.1
Net Income	32.2		32.2
Dividends on Common Shares	(22.6)		(22.6)
Shares Issued Under Stock Plans	1.7	1.7
Issuance of Common Shares	1.1	1.1
Ending Balance at Dec. 31, 2020	389	285.3	103.7
Net Income	36.1		36.1
Dividends on Common Shares	(23.6)		(23.6)
Shares Issued Under Stock Plans	1.3	1.3
Issuance of Common Shares	45.5	45.5
Ending Balance at Dec. 31, 2021	$ 448.3	$ 332.1	$ 116.2

CONSOLIDATED STATEMENTS OF CH_2

CONSOLIDATED STATEMENTS OF CHANGES IN COMMON STOCK EQUITY (Parenthetical) - $ / shares	Aug. 06, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Dividends per Common Share		$ 1.52	$ 1.50	$ 1.48
Common stock, shares issued	800,000	942,316	23,658	20,065

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
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 capital city areas 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 Maine to the Lewiston-Auburn area and in the greater Fitchburg area of north central Massachusetts. Unitil has three distribution Granite State is an interstate natural gas transmission pipeline company, 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, on May 1, 2003 Unitil Power ceased being the wholesale supplier of Unitil Energy 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. In the period since, Unitil Power continued to flow revenues and expenses from remaining contracts to Unitil Energy under the Amended Unitil System Agreement. The last of those contracts expired October 31, 2020, and the Company no longer has material revenues or expenses associated with those contracts. 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 Divestiture of Non-Regulated Business Subsidiary — million on this divestiture is included in Other Income (Expense), Net on the Consolidated Statements of Earnings for the year-ended December 31, 2019, while the income taxes associated with this transaction of million are included in the Provision For Income Taxes. Basis of Presentation Principles of Consolidation — Use of Estimates — Fair Value — Level 1— Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2— Valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly. Level 3— Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable. To the extent valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company’s own assumptions are set to reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may be reduced for many instruments. This condition could cause an instrument to be reclassified from Level 1 to Level 2 or from Level 2 to Level 3. There have been no changes in the valuation techniques used during the current period. Utility Revenue Recognition — Billed and unbilled revenue is recorded when service is rendered or energy is delivered to customers. However, the determination of energy sales to individual customers is based on the reading of their meters, which occurs on a systematic basis throughout the month. At the end of each calendar month, amounts of energy delivered to customers since the date of the last meter reading are estimated and the corresponding unbilled revenues are calculated. These unbilled revenues are estimated each month based on estimated customer usage by class and applicable customer rates, taking into account current and historical weather data, assumptions pertaining to metering patterns, billing cycle statistics, and other estimates and assumptions, and are then reversed in the following month when billed to customers. A majority of the Company’s revenue from contracts with customers continues to be recognized on a monthly basis based on applicable tariffs and customer monthly consumption. Such revenue is recognized using the invoice practical expedient which allows an entity to recognize revenue in the amount that directly corresponds to the value transferred to the customer. The Company’s billed and unbilled rev e In the following tables, revenue is classified by the types of goods/services rendered and market/customer type. Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 135.1 $ 83.9 $ 219.0 Commercial & Industrial 103.3 124.1 227.4 Other 10.1 9.6 19.7 Total Billed and Unbilled Revenue 248.5 217.6 466.1 Rate Adjustment Mechanism Revenue — 7.2 7.2 Total Electric and Gas Operating Revenues $ 248.5 $ 224.8 $ 473.3 Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 128.7 $ 73.1 $ 201.8 Commercial & Industrial 91.4 104.5 195.9 Other 6.6 7.6 14.2 Total Billed and Unbilled Revenue 226.7 185.2 411.9 Rate Adjustment Mechanism Revenue 0.5 6.2 6.7 Total Electric and Gas Operating Revenues $ 227.2 $ 191.4 $ 418.6 Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 121.5 $ 81.4 $ 202.9 Commercial & Industrial 93.8 120.1 213.9 Other 7.8 10.6 18.4 Total Billed and Unbilled Revenue 223.1 212.1 435.2 Rate Adjustment Mechanism Revenue 10.8 (8.7 ) 2.1 Total Electric and Gas Operating Revenues $ 233.9 $ 203.4 $ 437.3 Fitchburg is subject to revenue decoupling. Revenue decoupling is the term given to the elimination of the dependency of a utility’s distribution revenue on the volume of electricity or natural gas sales. The difference between distribution revenue amounts billed to customers and the targeted revenue decoupling amounts is recorded as an increase or a decrease in the current portion of Accrued Revenue, which forms the basis for resetting rates for future cash recoveries from, or credits to, customers. These revenue decoupling targets may be adjusted as a result of rate cases that the Company files with the Massachusetts Department of Public Utilities (MDPU). The Company estimates that revenue decoupling applies to approximately 27% and 11% of Unitil’s total annual electric and natural gas sales volumes, respectively. The Company bills its customers for sales tax in Massachusetts and Maine. These taxes are remitted to the appropriate departments of revenue in each state and are excluded from revenues on the Company’s Consolidated Statements of Earnings. Other Operating Revenue—Non-regulated — Depreciation and Amortization — Stock-based Employee Compensation — 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 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. Dividends y annualized dividend rates of $1.50 and $1.48 per common share, respectively. At its January 2022 meeting, the Unitil Corporation Board of Directors declared a quarterly dividend on the Company’s common stock of $0.39 per share, an increase of $0.01 per share on a quarterly basis, resulting in an increase in the effective annualized dividend rate to $1.56 per share from $1.52 per share. Cash and Cash Equivalents (ISO-NE) ISO-NE. 2-1/2 ISO-NE Financial Instruments 2016-13, Allowance for Doubtful Accounts — Accounts Receivable, Net includes $3.1 million and $3.1 million of the Allowance for Doubtful Accounts at December 31, 2021 and December 31, 2020, respectively. Unbilled Revenues, net (a component of Accrued Revenue) includes $0.2 million and $0.2 million of the Allowance for Doubtful Accounts at December 31, 2021 and December 31, 2020, respectively. Accrued Revenue— Accrued Revenue (millions) December 31, 2021 2020 Regulatory Assets—Current $ 47.4 $ 37.3 Unbilled Revenues 13.8 13.6 Total Accrued Revenue $ 61.2 $ 50.9 Exchange Gas Receivable — through March. The exchange and storage gas volumes are recorded at weighted average cost. The following table shows the components of Exchange Gas Receivable as of December 31, 2021 and 2020. Exchange Gas Receivable (millions) December 31, 2021 2020 Northern Utilities $ 6.7 $ 4.4 Fitchburg 0.7 0.5 Total Exchange Gas Receivable $ 7.4 $ 4.9 Gas Inventory Gas Inventory (millions) December 31, 2021 2020 Natural Gas $ 0.5 $ 0.2 Propane 0.4 0.3 Liquefied Natural Gas & Other 0.1 0.1 Total Gas Inventory $ 1.0 $ 0.6 The Company also has an inventory of Materials and Supplies in the amounts of $8.6 million and $8.5 million as of December 31, 2021 and December 31, 2020, respectively. These amounts are recorded at weighted average cost. Utility Plant Cost of additions consists of The costs of current repairs and minor replacements are charged to appropriate operating expense accounts. The original cost of utility plant retired or otherwise disposed of is charged to the accumulated provision for depreciation. The Company includes in its mass asset depreciation rates, which are periodically reviewed as part of its ratemaking proceedings, cost of removal amounts to provide for future negative salvage value. At December 31, 2021 and 2020, the Company has recorded cost of removal amounts of $107.5 million and $105.2 million, respectively, that have been collected in depreciation rates but have not yet been expended, and which represent regulatory liabilities. These amounts are recorded on the Consolidated Balance Sh e Regulatory Accounting — following table. Regulatory Assets consist of the following (millions) December 31, 2021 2020 Retirement Benefits $ 86.4 $ 103.7 Energy Supply & Other Rate Adjustment Mechanisms 44.1 34.1 Deferred Storm Charges 3.3 4.1 Environmental 4.6 5.2 Income Taxes 2.6 3.4 Other Deferred Charges 15.3 14.2 Total Regulatory Assets 156.3 164.7 Less: Current Portion of Regulatory Assets (1) 47.4 37.3 Regulatory Assets—noncurrent $ 108.9 $ 127.4 (1) Reflects amounts included in the Accrued Revenue on the Company’s Consolidated Balance Sheets. Regulatory Liabilities consist of the following (millions) December 31, 2021 2020 Rate Adjustment Mechanisms $ 7.7 $ 4.1 Income Taxes 44.3 45.5 Other 0.1 0.2 Total Regulatory Liabilities 52.1 49.8 Less: Current Portion of Regulatory Liabilities 9.5 5.5 Regulatory Liabilities—noncurrent $ 42.6 $ 44.3 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 December 31, 2021 are $8.5 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 effect 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 Regul a 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. Leases non-lease v 4 Derivatives — The Company had no derivative assets or liabilities recorded on its Consolidated Balance Sheets as of December 31, 2021 and December 31, 2020. There were no losses / (gains) recognized in Regulatory Assets / Liabilities for the years ended December 31, 2021 and 2020. There were no losses / (gains) reclassified into the Consolidated Statements of Earnings for the years ended December 31, 2021, 2020 and 2019. Fitchburg has entered into power purchase agreements for which contingencies exist (see “Fitchburg – Massachusetts RFP’s” section of Note 7 (Commitments and Contingencies). Until these contingencies are satisfied, these contracts will not qualify for derivative accounting. The Company believes that the power purchase obligations under these long-term contracts will have a material effect on the contractual obligations of Fitchburg. Investments in Marketable Securities — At December 31, 2021 and 2020, the fair value of the Company’s investments in these trading securities, which are recorded on the Consolidated Balance Sheets in Other Assets, were $5.7 million and $5.7 million, respectively, as shown in the following table. Fair Value of Marketable Securities (millions) December 31, 2021 2020 Money Market Funds $ 5.7 $ 5.7 Total Marketable Securities $ 5.7 $ 5.7 The Company also sponsors the Unitil Corporation Deferred Compensation Plan (the DC Plan). The DC Plan is a non-qualified tax-deferred participants to defer up to 85% of base salary, and up to 85% of any cash incentive for retirement. The Company may also elect to make discretionary contributions on behalf of any participant in an amount determined by the Company’s Board of Directors. A trust has been established to invest the funds associated with the DC Plan. At December 31, 2021 and 2020, the fair value of the Company’s investments in these trading securities related to the DC Plan, which are recorded on the Consolidated Balance Sheets in Other Assets, were $ million and $ million, respectively. 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 (Income) Expense, Net. Fair Value of Marketable Securities (millions) December 31, 2021 2020 Equity Funds $ 0.2 $ 0.2 Money Market Funds 0.4 0.3 Total Marketable Securities $ 0.6 $ 0.5 Energy Supply Obligations December 31, Energy Supply Obligations consist of the following: (millions) 2021 2020 Renewable Energy Portfolio Standards $ 7.8 $ 5.7 Exchange Gas Obligation 6.7 4.4 Power Supply Contract Divestitures — 0.3 Total Energy Supply Obligations $ 14.5 $ 10.4 Renewable Energy Portfolio Standards Fitchburg has e n Exchange Gas Obligation — Power Supply Contract Divestitures— o Retirement Benefit Obligations non-union non-qualified The Company records on its balance sheets as an asset or liability the overfunded or underfunded status of its retirement benefit obligations (RBO) based on the projected benefit obligations. The Company has recognized a corresponding Regulatory Asset, reflecting ultimate recovery from customers through rates. The regulatory asset (or regulatory liability) is amortized as the actuarial gains and losses and prior service cost are amortized to net periodic benefit cost for the Pension and PBOP plans. All amounts are remeasured annually. (See Note 9 Retirement Benefit Plans). Commitments and Contingencies 7 Environmental Matters 7 o Subsequent Events

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2021
Segment Information	Note 2: Segment Information Unitil reports three segments: utility electric operations, utility gas operations and non-regulated. 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 Maine to the Lewiston-Auburn area 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. Granite State is an interstate natural gas transmission pipeline company, 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 transmission services provided to Northern Utilities and, to a lesser extent, third-party marketers. Granite State is included in the utility gas operations segment. Unitil Resources is the Company’s wholly-owned non-regulated Non-Regulated Unitil Realty, Unitil Service and the holding company are included in Other. Unitil Service provides centralized management and administrative services, including information systems management and financial record keeping. Unitil Realty owns certain real estate, principally the Company’s corporate headquarters. The earnings of the holding company are principally derived from income earned on short-term investments and real property owned for Unitil and its subsidiaries’ use. The segments follow the same accounting policies as described in the Summary of Significant Accounting Policies. Intersegment sales take place at cost and the effects of all intersegment and/or intercompany transactions are eliminated in the consolidated financial statements. Segment profit or loss is based on profit or loss from operations after income taxes and preferred stock dividends. Expenses used to determine operating income before taxes are charged directly to each segment or are allocated based on cost allocation factors included in rate applications approved by the FERC, NHPUC, MDPU, and MPUC. Assets allocated to each segment are based upon specific identification of such assets provided by Company records. The following tables provide significant segment financial data for the years ended December 31, 2021, 2020 and 2019 (millions) : Year Ended December 31, 2021 Electric Gas Non- Other Total Revenues: Billed and Unbilled Revenue $ 248.5 $ 217.6 $ — $ — $ 466.1 Rate Adjustment Mechanism Revenue — 7.2 — — 7.2 Total Operating Revenues 248.5 224.8 — — 473.3 Interest Income 0.8 0.5 — 0.3 1.6 Interest Expense 9.0 15.3 — 2.9 27.2 Depreciation & Amortization Expense 25.9 32.6 — 1.0 59.5 Income Tax Expense (Benefit) 4.5 7.7 (0.1 ) (0.6 ) 11.5 Segment Profit (Loss) 14.0 23.2 0.1 (1.2 ) 36.1 Segment Assets 584.0 935.9 — 20.4 1,540.3 Capital Expenditures 38.1 75.8 — 1.1 115.0 Year Ended December 31, 2020 Revenues: Billed and Unbilled Revenue $ 226.7 $ 185.2 $ — $ — $ 411.9 Rate Adjustment Mechanism Revenue 0.5 6.2 — — 6.7 Total Operating Revenues 227.2 191.4 — — 418.6 Interest Income 1.1 1.1 — 0.4 2.6 Interest Expense 8.7 14.2 — 3.5 26.4 Depreciation & Amortization Expense 23.8 29.8 — 0.9 54.5 Income Tax Expense (Benefit) 4.7 7.3 — (1.8 ) 10.2 Segment Profit 12.9 19.3 — — 32.2 Segment Assets 571.8 886.3 — 19.8 1,477.9 Capital Expenditures 45.5 71.1 — 6.0 122.6 Year Ended December 31, 2019 Revenues: Billed and Unbilled Revenue $ 223.1 $ 212.1 $ — $ — $ 435.2 Rate Adjustment Mechanism Revenue 10.8 (8.7 ) — — 2.1 Other Operating Revenue—Non-Regulated — — 0.9 — 0.9 Total Operating Revenues 233.9 203.4 0.9 — 438.2 Interest Income 0.9 1.2 0.2 0.6 2.9 Interest Expense 9.4 14.4 — 2.8 26.6 Depreciation & Amortization Expense 22.6 28.5 — 0.9 52.0 Income Tax Expense (Benefit) 4.2 7.2 3.8 (1.4 ) 13.8 Segment Profit 11.5 19.1 10.2 3.4 44.2 Segment Assets 529.3 823.3 0.3 17.9 1,370.8 Capital Expenditures 39.6 74.0 — 5.6 119.2

Allowance for Doubtful Accounts

Allowance for Doubtful Accounts	12 Months Ended
	Dec. 31, 2021
Allowance For Doubtful Accounts [Abstract]
Allowance for Doubtful Accounts	Note 3: Allowance for Doubtful Account s Unitil’s distribution utilities are authorized by regulators to recover the costs of their energy commodity portion of bad debts through rate mechanisms. In 2021, 2020 and 2019, the Company recorded provisions for the energy commodity portion of bad debts of $2.4 million, $1.6 million and $2.3 million, respectively. These provisions were recognized in Cost of Electric Sales and Cost of Gas Sales expense as the associated electric and gas utility revenues were billed. Cost of Electric Sales and Cost of Gas Sales costs are recovered from customers through periodic rate reconciling mechanisms. Also, the electric and gas divisions of Fitchburg are authorized to recover through rates past due amounts associated with hardship accounts that are protected from shut-off. future Accounts Receivable, Net includes $3.1 million and $3.1 million of the The following table shows the balances and activity in the Company’s Allowance for Doubtful Accounts for 2021, 2020 and 2019 (millions): ALLOWANCE FOR DOUBTFUL ACCOUNTS Balance at Provision Recoveries Accounts Regulatory Deferrals* Balance at Year Ended December 31, 2021 Electric $ 1.6 $ 3.3 $ 0.4 $ 3.4 $ 0.1 $ 2.0 Gas 1.7 2.3 0.4 3.1 — 1.3 Other — — — — — — $ 3.3 $ 5.6 $ 0.8 $ 6.5 $ 0.1 $ 3.3 Year Ended December 31, 2020 Electric $ 0.6 $ 2.9 $ 0.3 $ 2.6 $ 0.4 $ 1.6 Gas 0.4 2.6 0.3 1.8 0.2 1.7 Other — — — — — — $ 1.0 $ 5.5 $ 0.6 $ 4.4 $ 0.6 $ 3.3 Year Ended December 31, 2019 Electric $ 0.5 $ 3.0 $ 0.3 $ 3.2 $ — $ 0.6 Gas 0.8 1.9 0.5 2.8 — 0.4 Other — — — — — — $ 1.3 $ 4.9 $ 0.8 $ 6.0 $ — $ 1.0 * The Company has incurred greater than normal bad debt expense due to the coronavirus pandemic. Incremental bad debt expense amounts have been deferred as regulatory assets based on certain regulatory proceedings and management’s belief that such amounts are probable of recovery (See the “Financial Effects of COVID-19 7

Debt and Financing Arrangements

Debt and Financing Arrangements	12 Months Ended
	Dec. 31, 2021
Debt Disclosure [Abstract]
Debt and Financing Arrangements	Note 4: Debt and Financing Arrangements The Company funds a portion of its operations through the issuance of long-term debt, and short-term borrowings under its revolving Credit Facility. The Company’s subsidiaries conduct a portion of their operations in leased facilities and lease some of their machinery, vehicles and office equipment. Long-Term Debt and Interest Expense Long-Term Debt Structure and Covenants — The long-term debt of Unitil is issued under Unsecured Promissory Notes with negative s Substantially all of the property of Unitil Energy is subject to liens of indenture under which First Mortgage Bonds (FMB) have been issued. In order to issue new FMB, the customary covenants of the existing Unitil Energy Indenture Agreement must be met, including that Unitil Energy have sufficient available net bondable plant to issue the securities and earnings available for interest charges equal to at least two times the annual interest requirement. The Unitil Energy agreements further require that if Unitil Energy defaults on any Unitil Energy FMB, it would constitute a default for all Unitil Energy FMB. The Unitil Energy default provisions are not triggered by the actions or defaults of Unitil or its other subsidiaries. All of the long-term debt of Fitchburg, Northern Utilities and Granite State are issued under Unsecured Promissory Notes with negative pledge provisions. Each issue of long-term debt ranks pari passu with its other senior unsecured long-term debt within that subsidiary. The long-term debt’s negative pledge provisions contain restrictions which, among other things, limit the incursion of additional long-term debt. Accordingly, in order for Fitchburg, Northern Utilities or Granite State to issue new long-term debt, the covenants of the existing long-term agreements of that subsidiary must be satisfied, including that the subsidiary have total funded indebtedness less than 65% of total capitalization. Additionally, to issue new long-term debt, Fitchburg must maintain earnings available for interest equal to at least two times the interest charges for funded indebtedness. As with the Unitil Energy agreements, the Fitchburg, Northern Utilities and Granite State long-term debt agreements each require that if that subsidiary defaults on any of its own long-term debt agreements, it would constitute a default under all of that subsidiary’s long-term debt agreements. None of the Fitchburg, Northern Utilities and Granite State default provisions are triggered by the actions or defaults of Unitil or any of its other subsidiaries. The Unitil, Unitil Energy, Fitchburg, Northern Utilities and Granite State long-term debt instruments and agreements contain covenants restricting the ability of each company to incur liens and to enter into sale and leaseback transactions, and restricting the ability of each company to consolidate with, to merge with or into, or to sell or otherwise dispose of all or substantially all of its assets. Unitil Energy, Fitchburg, Northern Utilities and Granite State pay common dividends to their sole common shareholder, Unitil Corporation and these common dividends are the primary source of cash for the payment of dividends to Unitil’s common shareholders. The long-term debt issued by the Company and its subsidiaries contains certain covenants that determine the amount that the Company and each of these subsidiary companies has available to pay for dividends. As of December 31, 2021, in accordance with the covenants, these subsidiary companies had a combined amount of $358.7 million available for the payment of dividends and Unitil Corporation had $166.9 million available for the payment of dividends. As of December 31, 2021, the Company’s balance in Retained Earnings was $116.2 million. Therefore, there were no restrictions on the Company’s Retained Earnings at December 31, 2021 for the payment of dividends. Issuance of Long-Term Debt purposes On September 15, 2020, Northern Utilities issued $40 million of Notes due 2040 at 3.78%. Fitchburg issued $27.5 On December 18, 2019, Unitil Corporation issued $30 million of Notes due 2029 at 3.43%. Unitil Corporation used the net proceeds from this offering to repay short-term debt and for general corporate purposes. Approximately $0.2 million of costs associated with these issuances have been recorded as a reduction to Long-Term Debt for presentation purposes on the Consolidated Balance Sheets. On September 12, 2019, Northern Utilities issued $40 million of Notes due 2049 at 4.04%. Northern Utilities used the net proceeds from this offering to repay short-term debt and for general corporate purposes. Approximately $0.2 million of costs associated with these issuances have been recorded as a reduction to Long-Term Debt for presentation purposes on the Consolidated Balance Sheets. Debt Repayment The aggregate amount of bond repayment requirements and normal scheduled long-term debt repayments for each of the five years following 2021 is: 2022 – $ – $ – $ – $ million; – $ Fair Value of Long-Term Debt Estimated Fair Value of Long-Term Debt (millions) December 31, 2021 2020 Estimated Fair Value of Long-Term Debt $ 584.9 $ 633.1 Details on long-term debt at December 31, 2021 and 2020 are shown below: Long-Term Debt (millions) December 31, 2021 2020 Unitil Corporation: 6.33% Senior Notes, Due May 1, 2022 $ — $ 15.0 3.70% Senior Notes, Due August 1, 2026 30.0 30.0 3.43% Senior Notes, Due December 18, 2029 30.0 30.0 Unitil Energy First Mortgage Bonds: 8.49% Senior Secured Notes, Due October 14, 2024 1.5 3.0 6.96% Senior Secured Notes, Due September 1, 2028 14.0 16.0 8.00% Senior Secured Notes, Due May 1, 2031 15.0 15.0 6.32% Senior Secured Notes, Due September 15, 2036 15.0 15.0 3.58% Senior Secured Notes, Due September 15, 2040 27.5 27.5 4.18% Senior Secured Notes, Due November 30, 2048 30.0 30.0 Fitchburg: 6.75% Senior Notes, Due November 30, 2023 — 1.9 6.79% Senior Notes, Due October 15, 2025 6.0 10.0 3.52% Senior Notes, Due November 1, 2027 10.0 10.0 7.37% Senior Notes, Due January 15, 2029 9.6 10.8 5.90% Senior Notes, Due December 15, 2030 15.0 15.0 7.98% Senior Notes, Due June 1, 2031 14.0 14.0 3.78% Senior Notes, Due September 15, 2040 27.5 27.5 4.32% Senior Notes, Due November 1, 2047 15.0 15.0 Northern Utilities: 3.52% Senior Notes, Due November 1, 2027 20.0 20.0 7.72% Senior Notes, Due December 3, 2038 50.0 50.0 3.78% Senior Notes, Due September 15, 2040 40.0 40.0 4.42% Senior Notes, Due October 15, 2044 50.0 50.0 4.32% Senior Notes, Due November 1, 2047 30.0 30.0 4.04% Senior Notes, Due September 12, 2049 40.0 40.0 Granite State: 3.72% Senior Notes, Due November 1, 2027 15.0 15.0 Unitil Realty Corp.: 2.64% Senior Secured Notes, Due December 18, 2030 4.5 4.7 Total Long-Term Debt 509.6 535.4 Less: Unamortized Debt Issuance Costs 3.6 3.8 Total Long-Term Debt, net of Unamortized Debt Issuance Costs 506.0 531.6 Less: Current Portion (1) 8.2 8.5 Total Long-Term Debt, Less Current Portion $ 497.8 $ 523.1 (1) The Current Portion of Long-Term Debt includes sinking fund payments. Interest Expense, Net d. Unitil’s utility subsidiaries operate a number of reconciling rate mechanisms to recover specifically identified costs on a pass-through basis. These reconciling rate mechanisms track costs and revenue on a monthly basis. In any given month, this monthly tracking and reconciling process will produce either an under-collected or an over-collected balance of costs. In accordance with the distribution utilities’ rate tariffs, interest is accrued on these balances and will produce either interest income or interest expense. Consistent with regulatory precedent, interest income is recorded on an under-collection of costs, which creates a regulatory asset to be recovered in future periods when rates are reset. Interest expense is recorded on an over-collection of costs, which creates a regulatory liability to be refunded Interest Expense, Net (millions) 2021 2020 2019 Interest Expense Long-Term Debt $ 26.0 $ 24.8 $ 22.9 Short-Term Debt 0.8 1.4 3.0 Regulatory Liabilities 0.4 0.2 0.7 Subtotal Interest Expense 27.2 26.4 26.6 Interest Income Regulatory Assets (0.5 ) (0.8 ) (0.8 ) AFUDC (1) (1.1 ) (1.8 ) (2.1 ) Subtotal Interest Income (1.6 ) (2.6 ) (2.9 ) Total Interest Expense, Net $ 25.6 $ 23.8 $ 23.7 (1) AFUDC—Allowance for Funds Used During Construction Credit Arrangements On July 25, 2018, the Company entered into a Second Amended and Restated Credit Agreement (the “Credit Facility”) with a syndicate of lenders, which amended and restated in its entirety the Company’s prior credit agreement, dated as of October 4, 2013, as amended. The Credit Facility extends to July 25, 2023, subject to two one-year one-month The Company utilizes the Credit Facility for cash management purposes related to its short-term operating activities. Total gross borrowings were $239.1 million and $248.9 million for the years ended December 31, 2021 and December 31, 2020, respectively. Total gross repayments were $229.7 million and $252.8 million for the years ended December 31, 2021 and December 31, 2020, respectively. The following table details the borrowing limits, amounts outstanding and amounts available under the revolving Credit Facility as of December 31, 2021 and December 31, 2020: Revolving Credit Facility (millions) December 31, 2021 2020 Limit $ 120.0 $ 120.0 Short-Term Borrowings Outstanding $ 64.1 $ 54.7 Letters of Credit Outstanding $ — $ 0.1 Available $ 55.9 $ 65.2 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’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 to Unitil 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 Unitil’s Funded Debt to Capitalization (as each term is defined in the Credit Facility) cannot exceed 65%, tested on a quarterly basis. At December 31, 2021 and December 31, 2020, the Company was in compliance with the covenants contained in the Credit Facility in effect on that date. The Company believes i The weighted average interest rates on all short-term borrowings were 1.2%, 1.7%, and 3.4% during 2021, 2020, and 2019, respectively. 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. In April 2014, Unitil Service entered into a financing arrangement, structured as a 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 $8.3 million and $5.4 million of natural gas storage inventory at December 31, 2021 and 2020, respectively, related to these asset management agreements. The amount of natural gas inventory released in December 2021, which was payable in January 2022, was $1.6 million and was recorded in Accounts Payable at December 31, 2021. The amount of natural gas inventory released in December 2020, which was payable in January 2021, was $1.0 million and was recorded in Accounts Payable at December 31, 2020. Contractual Obligations The following table lists the Company’s contractual obligations for long-term debt as of December 31, 2021. Payments Due by Period Long-Term Debt Contractual Obligations (millions) as of December 31, 2021 Total 2022 2023 2024 2025 2026 2027 & Long-Term Debt $ 509.6 $ 8.4 $ 6.9 $ 6.9 $ 5.0 $ 38.0 $ 444.4 Interest on Long-Term Debt 360.5 24.5 23.9 23.4 22.9 22.6 243.2 Total $ 870.1 $ 32.9 $ 30.8 $ 30.3 $ 27.9 $ 60.6 $ 687.6 Leases Unitil’s subsidiaries lease some of their vehicles, machinery and office equipment under both capital and operating lease arrangements. Total rental expense under operating leases charged to operations for the years ended December 31, 2021, 2020 and 2019 amounted December 31, Lease Obligations (millions) 2021 2020 Operating Lease Obligations: Other Current Liabilities (current portion) $ 1.6 $ 1.5 Other Noncurrent Liabilities (long-term portion) 3.1 3.7 Total Operating Lease Obligations 4.7 5.2 Capital Lease Obligations: Other Current Liabilities (current portion) 0.1 0.2 Other Noncurrent Liabilities (long-term portion) 0.2 0.2 Total Capital Lease Obligations 0.3 0.4 Total Lease Obligations $ 5.0 $ 5.6 Cash paid for amounts included in the measurement of operating lease obligations for the twelve months ended December 31, 2021 and 2020 w as as Assets under capital leases amounted to approximately $0.7 million and $1.0 million as of December 31, 2021 and 2020, respectively, less accumulated amortization of $0.3 million and $0.5 million, respectively and are included in Net Utility Plant on the Company’s Consolidated Balance Sheet s. The following table is a schedule of future operating lease payment obligations and future minimum lease payments under capital leases as of December 31, 2021. The payments for operating leases consist of $1.6 million of current operating lease obligations, which are included in Other Current Liabilities and $3.1 million of noncurrent operating lease obligations, which are included in Other Noncurrent Liabilities, on the Company’s Consolidated Balance Sheets as of December 31, 2021. The payments for capital leases consist of $0.1 million of current Capital Lease Obligations Lease Payments ($000’s) Year Ending December 31, Operating Capital 2022 $ 1,695 $ 150 2023 1,399 107 2024 1,069 52 2025 503 19 2026 199 — 2027-2031 121 — Total Payments 4,986 328 Less: Interest 316 12 Amount of Lease Obligations Recorded on Consolidated Balance Sheets $ 4,670 $ 316 Operating lease obligations are based on the net present value of the remaining lease payments over the remaining lease term. In determining the present value of lease payments, the Company used the interest rate stated in each lease agreement. As of December 31, 2021, the weighted average remaining lease term is 3.5 years and the weighted average operating discount rate used to determine the operating lease obligations was 3.9%. As of December 31, 2020, the weighted average remaining lease term was 3.8 years and the weighted average operating discount rate used to determine the operating lease obligations was 4.4%. Guarantees The Company provides limited guarantees on

Equity

Equity	12 Months Ended
	Dec. 31, 2021
Equity	Note 5: Equity The Company has common stock outstanding and one of our subsidiaries has preferred stock outstanding. Common Stock The Company’s common stock trades on the New York Stock Exchange under the symbol “UTL”. The Company had 15,977,766 and 15,012,310 shares of common stock outstanding at December 31, 2021 and December 31, 2020, respectively. The Company has 25,000,000 shares of common stock authorized as of December 31, 2021 and December 31, 2020. Unitil Corporation Common Stock Offering The Company’s net increase to Common Equity and Cash proceeds from the Offering was approximately $38.6 million. The proceeds were used to make equity capital contributions to the Company’s regulated utility subsidiaries, to repay debt and for other general corporate purposes. As part of the Offering, the Company granted the underwriters a 30-day Dividend Reinvestment and Stock Purchase Plan Common Shares Repurchased, Cancelled and Retired 10b5-1 10b5-1 During 2021, 2020 and 2019, the Company did not cancel or retire any of its common stock. Stock-Based Compensation Plans 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. 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 or retirement. Restricted Shares issued for 2019 – 2021 in conjunction with the Stock Plan are presented in the following table: Issuance Date Shares Aggregate 1/29/19 33,150 $1.6 1/28/20 28,630 $1.8 7/28/20 3,000 $0.1 1/26/21 23,140 $0.9 There were 37,621 and 39,426 non-vested 25 market value of $1.7 million. Restricted Stock Units Restricted Stock Units, which are issued to The equity portion of Restricted Stock Units activity during 2021 and 2020 in conjunction with the Stock Plan are presented in the following table: Restricted Stock Units (Equity Portion) 2021 2020 Units Weighted Units Weighted Beginning Restricted Stock Units 43,192 $ 41.34 70,364 $ 41.20 Restricted Stock Units Granted 4,519 $ 43.35 3,743 $ 39.26 Dividend Equivalents Earned 1,471 $ 46.34 1,507 $ 47.34 Restricted Stock Units Settled — $ — (32,422 ) $ 41.09 Ending Restricted Stock Units 49,182 $ 41.67 43,192 $ 41.34 Other Noncurrent Liabilities on the Company’s Consolidated Balance Sheets as of December 31, 2021 and 2020 include o Preferred Stock There were $0.2 million, or 1,861 shares, of Unitil Energy’s 6.00% Series Preferred Stock outstanding as of December 31, 2021. There were $0.2 million, or 1,887 shares, of Unitil Energy’s 6.00% Series Preferred Stock outstanding as of December 31, 2020. There were less than $0.1 million of total dividends declared on Preferred Stock in each of the twelve month periods ended December 31, 2021 and December 31, 2020, respectively. Earnings Per Share The following table reconciles basic and diluted earnings per share (EPS). (Millions except shares and per share data) 2021 2020 2019 Earnings Available to Common Shareholders $ 36.1 $ 32.2 $ 44.2 Weighted Average Common Shares Outstanding—Basic (000’s) 15,373 14,951 14,894 Plus: Diluted Effect of Incremental Shares (000’s) 3 1 6 Weighted Average Common Shares Outstanding—Diluted (000’s) 15,376 14,952 14,900 Earnings per Share—Basic and Diluted $ 2.35 $ 2.15 $ 2.97 The following table shows the number of weighted average non-vested 2021 2020 2019 Weighted Average Non-Vested 23,636 42,813 —

Energy Supply

Energy Supply	12 Months Ended
	Dec. 31, 2021
Energy Supply [Abstract]
Energy Supply	Note 6: Energy Supply ELECTRIC POWER SUPPLY Fitchburg, Unitil Energy, and Unitil Power each are members of the New England Power Pool (NEPOOL) and participate in the Independent System Operator—New England (ISO-NE) Unitil’s customers in both New Hampshire and Massachusetts are entitled to purchase their electric supply from competitive third-party suppliers. As of December 2021, nearly 77% of Unitil’s largest New Hampshire customers, representing 22% of Unitil’s New Hampshire electric kilowatt-hour (kWh) sales, and 80% of Unitil’s largest Massachusetts customers, representing 34% of Unitil’s Massachusetts electric kWh sales, purchased their electric power supply in the competitive market. Additionally, cities and towns in Massachusetts may, with approval from the MDPU, implement municipal aggregations whereby the municipality purchases electric power on behalf of all citizens and businesses that do not opt out of the aggregation. The Towns of Lunenburg and Ashby have active municipal aggregations. Customers in Lunenburg comprise about 17% of Fitchburg’s customer base, and customers in Ashby comprise another 4%. On December 31, 2020, the City of Fitchburg filed with the MDPU for approval of its Aggregation Plan. The aggregation is anticipated to be implemented in mid-2022. The City of Fitchburg comprises about 69% of Company sales. As of December 2021, 27% of Unitil’s residential customers in Massachusetts purchased their electricity from a third-party supplier. In New Hampshire, the percentage of residential customers purchasing electricity from a third-party supplier in 2021 is 7.8%, down 0.5 % from 8.3% in 2020 and reflecting a downward trend from a high of 13% in 2015. Most residential and small commercial customers continue to purchase their electric supply through Unitil’s electric distribution utilities under regulated energy rates and tariffs. Municipal aggregation is now provided for in New Hampshire, but no aggregations have begun in Unitil Energy’s service area. Regulated Electric Power Supply To provide regulated electric supply service to their customers, Unitil’s electric distribution utilities enter into load-following wholesale electric power supply contracts to purchase electric supply from various wholesale suppliers. Unitil Energy currently has power supply contracts with various wholesale suppliers for the provision of Default Service to its customers. Currently, with approval of the NHPUC, Unitil Energy purchases Default Service power supply contracts for small, medium and large customers every six months for 100% of the supply requirements. Fitchburg has power supply contracts with various wholesale suppliers for the provision of Basic Service electric supply. MDPU policy establishes the pricing structure and duration of each of these contracts. Basic Service power supply contracts for residential and for small and medium general service customers are acquired every six months, are 12 months in duration and provide 50% of the supply requirements. On June 13, 2012, the MDPU approved Fitchburg’s request to discontinue the procurement process for Fitchburg’s large customers and become the load-serving entity for these customers. Currently, all Basic Service power supply requirements for large accounts are assigned to Fitchburg’s ISO-NE ISO-NE’s The NHPUC and MDPU regularly review alternatives to their procurement policy, which may lead to future changes in this regulated power supply procurement structure. Regional Electric Transmission and Power Markets Fitchburg, Unitil Energy and Unitil Power, as well as virtually all New England electric utilities, are participants in the ISO-NE ISO-NE ISO-NE ISO-NE ISO-NE Electric Power Supply Divestiture In connection with the implementation of retail choice, Unitil Power, which formerly functioned as the wholesale power supply provider for Unitil Energy, and Fitchburg divested their long-term power supply contracts through the sale of the entitlements to the electricity sold under those contracts. Unitil Energy and Fitchburg recover in their rates all the costs associated with the divestiture of their power supply portfolios and have secured regulatory approval from the NHPUC and MDPU, respectively, for the recovery of power supply-related stranded costs and other restructuring-related regulatory assets. The companies have a continuing obligation to submit regulatory filings that demonstrate their compliance with regulatory mandates and provide for timely recovery of costs in accordance with their approved restructuring plans. NATURAL GAS SUPPLY Unitil purchases and manages gas supply for customers served by Northern Utilities in Maine and New Hampshire, and by Fitchburg in Massachusetts. Northern Utilities’ Commercial and Industrial (C&I) customers are entitled to purchase their natural gas supply from third-party gas suppliers. Many of Northern Utilities’ large, and some of its medium, C&I customers purchase their gas supply from third-party suppliers. Most small C&I customers, and all residential customers, purchase their gas supply from Northern Utilities under regulated rates and tariffs. As of December 2021, 74% of Unitil’s largest New Hampshire gas customers, representing 39% of Unitil’s New Hampshire gas therm sales, and 63% of Unitil’s largest Maine customers, representing 24% of Unitil’s Maine gas therm sales, purchased their gas supply from a third-party supplier. Fitchburg’s residential and C&I business customers are entitled to purchase their natural gas supply from third-party gas suppliers. Many of Fitchburg’s large, and some of its medium, C&I customers, purchase their gas supply from third-party suppliers. Most of Fitchburg’s residential and small C&I customers continue to purchase their supplies at regulated rates from Fitchburg. As of December 2021, 67% of Unitil’s largest Massachusetts gas customers, representing 27% of Unitil’s Massachusetts gas therm sales, purchased their gas supply from third-party suppliers. The approved costs associated with natural gas supplied to customers who do not contract with third-party suppliers are recovered on a pass-through basis through periodically adjusted rates, and are included in Cost of Gas Sales in the Consolidated Statements of Earnings. Regulated Natural Gas Supply Northern Utilities purchases the majority of its natural gas from U.S. domestic and Canadian suppliers largely under contracts of one year or less, and on occasion from producers and marketers on the spot market. Northern Utilities arranges for gas transportation and delivery to its system through its own long-term contracts with various interstate pipeline and storage facilities, through peaking supply contracts delivered to its system, or in the case of liquefied natural gas (LNG), via trucking of supplies to storage facilities within Northern Utilities’ service territory. Northern Utilities has available under firm contract 122,000 million British Thermal Units (MMbtu) per day of year-round and seasonal transportation capacity to its distribution facilities, and 4.3 billion cubic feet (BCF) of underground storage. As a supplement to pipeline natural gas, Northern Utilities owns an LNG storage and vaporization facility. This plant is used principally during peak load periods to augment the supply of pipeline Fitchburg purchases natural gas under contracts from producers and marketers largely under contracts of one year or less, and occasionally on the spot market. Fitchburg arranges for gas transportation and delivery to its system through its own long-term contracts with Tennessee Gas Pipeline, through peaking supply contracts delivered to its system, or in the case of LNG or liquefied propane gas (LPG), via trucking of supplies to storage facilities within Fitchburg’s service territory. Fitchburg has available under firm contract 14,439 MMbtu per day of year-round transportation and 0.4 BCF of underground storage capacity to its distribution facilities. As a supplement to pipeline natural gas, Fitchburg owns a propane air gas plant and an LNG storage and vaporization facility. These plants are used principally during peak load periods to augment the supply of pipeline natural gas.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 7: Commitments and Contingencie s Regulatory Matters Overview —Unitil’s distribution utilities deliver electricity and/or natural gas to customers in the Company’s service territories at rates established under traditional cost of service regulation. Under this regulatory structure, Unitil Energy, Fitchburg, and Northern Utilities are provided the opportunity to recover the cost of providing distribution service to their customers based on a representative test year, in addition to earning a return on their capital investment in utility assets. Fitchburg’s electric and gas divisions also operate under revenue decoupling mechanisms. Most of Unitil’s customers are entitled to purchase their electric or natural gas supplies from third-party suppliers. For Northern Utilities, only business customers are entitled to purchase their natural gas supplies from third-party suppliers at this time. Most small and medium-sized customers, however, continue to purchase such supplies through Unitil Energy, Fitchburg and Northern Utilities as the providers of basic or default service energy supply. Unitil Energy, Fitchburg and Northern Utilities purchase electricity or natural gas for basic or default service from unaffiliated wholesale suppliers and recover the actual costs of these supplies, without profit or markup, through reconciling, pass-through rate mechanisms that are periodically adjusted. The MDPU, the NHPUC and the MPUC each have continued to approve these reconciling rate mechanisms which allow Fitchburg, Unitil Energy and Northern Utilities to recover their actual wholesale energy costs for electric power and natural gas. In connection with the implementation of retail choice, Unitil Power and Fitchburg divested their long-term power supply contracts through the sale of the entitlements to the electricity sold under those contracts. Unitil Energy and Fitchburg recover in their rates all the costs associated with the divestiture of their power supply portfolios and have secured regulatory approval from the NHPUC and MDPU, respectively, for the recovery of power supply-related stranded costs and other restructuring-related regulatory assets. As of December 31, 2021, Fitchburg and Unitil Energy have fully recovered their power supply-related stranded costs. The obligations for prior periods related to these divestitures are recorded in Energy Supply Obligations on the Company’s Consolidated Balance Sheets with a corresponding regulatory asset recorded in Accrued Revenue. Unitil’s distribution companies have a continuing obligation to submit filings in Massachusetts and New Hampshire demonstrating their compliance with regulatory mandates and provide for timely recovery of costs in accordance with their approved restructuring plans. Ta On December 22, 2017, the Tax Cuts and Jobs Act of 2017 (TCJA) was signed into law. Among other things, the TCJA substantially reduced the corporate income tax rate to 21 %, effective January 1, 2018. Each state public utility commission, with jurisdiction over the areas that are served by Unitil’s electric and gas subsidiary companies, issued orders directing how the tax law changes were to be reflected in rates. Unitil has complied with these orders and has made the required changes to its rates as directed by the commissions. The FERC issued a Notice of Proposed Rulemaking that would allow it to determine which pipelines under the Natural Gas Act may be collecting unjust and unreasonable rates in light of the corporate tax reduction. This matter was resolved for Granite State in its May 2, 2018 uncontested rate settlement filing, which accounted for the effect of the TCJA. On November 21 , 2019, the FERC issued Order No. 864, a final rule on Public Utility Transmission Rate Changes to Address Accumulated Deferred Income Taxes. The new rule requires public utilities with formula transmission rates to revise their formula rates to include a transparent methodology to address the TCJA and future tax law changes on customer rates by accounting for “excess” or “deficient” Accumulated Deferred Income Taxes (ADIT). The FERC also required transmission providers with stated rates to account for TCJA’s effect on ADIT in their next rate case. The Company is complying with the new rule and there is no material effect on its financial position, operating results, or cash flows. Rate Case Activity Northern Utilities—Base Rates—Maine debt. As part of the order and increase in base revenue, the MPUC provided for recovery of some, but not all, of the Company’s implementation costs associated with its customer information system pending the completion of an investigation, including a third-party audit. On March 9, 2021, the MPUC opened a new docket to investigate the amount of customer information system costs that will be allowed in rates. On January 27, 2022, the Company and the Maine Office of the Public Advocate filed a stipulation in this docket. The stipulation includes no finding of imprudence or asset disallowance. The terms of the stipulation provide for recovery of the revenue requirement related to the Company’s customer information system in base rates starting November 1, 2022, which coincides with the timing of the Company’s winter cost of gas rate change. The stipulation is subject to approval by the MPUC. Northern Utilities—Targeted Infrastructure Replacement Adjustment (TIRA)—Maine Northern Utilities—Base Rates—New Hampshire which represents an increase of 8.1% over total annual revenue at present rates. The multi-year rate filing includes a revenue decoupling mechanism and an Arrearage Management Program for financial hardship customers. Northern Utilities also requested implementation of temporary rates for service rendered on and after October 1, 2021. On September 30, 2021, the NHPUC approved a settlement providing for a temporary rate increase of $2.6 million, effective October 1, 2021. As provided by statute, once a final order on permanent rates is issued, the permanent rate level is reconciled back to the effective date of the temporary rates Unitil Energy—Base Rates— Fitchburg—Base Rates—Electric million associated with its 2019 capital expenditures. The Department allowed the associated rate increase to become effective on January 1, 2021, subject to further investigation and reconciliation. On June 15, 2021, final approval of the filing was issued. On November 2, 2021, Fitchburg filed its cumulative revenue requirement of $ million associated with its 2019 and 2020 capital expenditures. The Department allowed the associated rate increase to become effective on January 1, 2022, subject to further investigation and reconciliation. On April 17, 2020, the MDPU approved a settlement agreement entered into by the Company and the Massachusetts Office of the Attorney General providing for a distribution increase of $1.1 million, effective November 1, 2020. The Company’s subsequent Compliance Filing reflected an adjusted distribution increase of $0.9 million, a decrease of $0.2 million from the original settlement amount. On May 21, 2020, the MDPU approved the Company’s Compliance Filing. The agreement provides for a Return on Equity of 9.7% and a capital structure reflecting 52.45% equity and 47.55% long-term debt. Under the agreement, the Company will not increase or redesign base distribution rates to become effective prior to November 1, 2023, though the Company may seek cost recovery for certain exogenous events that meet a revenue threshold of $0.1 million. The agreement also provides for the implementation of a major storm reserve fund, whereby the Company may recover the costs of restoration for qualifying storm events. In addition, the agreement provides for the extension of the annual capital cost recovery mechanism, modified to allow the recovery of property tax on the cumulative net capital expenditures.​​​​​​​ Fitchburg—Base Rates—Gas — On February 28, 2020, the MDPU approved a settlement agreement between the Company and the Massachusetts Office of the Attorney General. The agreement provides for an annual distribution revenue increase of $4.6 million to be phased in over two years: (1) an increase of $3.7 million, which became effective on March 1, 2020; and (2) an increase of $0.9 million, which became effective on March 1, 2021. Under the agreement, the Company will not increase or redesign base distribution rates to become effective prior to March 1, 2023, though the Company may seek cost recovery for certain exogenous events that meet a revenue effect threshold of $40,000. The agreement provides for a Return on Equity of 9.7% and a capital structure reflecting 52.45% equity and 47.55% long-term debt. Fitchburg—Gas System Enhancement Program — Granite State—Base Rates On August 24, 2021, the FERC accepted Granite State’s first limited Section 4 rate adjustment pursuant to the Settlement Agreement, for an annual revenue increase of $0.1 million, effective September 1, 2021. Other Matters Fitchburg—Grid Modernization , Fitchburg—Grid Modernization Cost Recovery Factor — Fitchburg—Investigation into the role of gas LDCs to achieve Commonwealth 2050 climate goals— net-zero net-zero Financial Effects of COVID-19 Pandemic — Northern Utilities / Granite State—Firm Capacity Contract — Reconciliation Filings — Fitchburg—Massachusetts Request for Proposals (RFPs)— The EDCs issued the RFP for Section 83D Long-Term Contracts for Qualified Clean Energy Projects in March 2017, and after selection of final projects and negotiation, final contracts for 9,554,940 % of the contract payments is reasonable and in the public interest and approved the EDCs’ proposal to amend their respective tariffs to include the recovery of costs associated with the contracts. The Massachusetts Supreme Judicial Court upheld the MDPU’s approval in an opinion dated September 3, 2020. The Company believes the power purchase obligations under these long-term contracts will have a material effect on the contractual obligations of Fitchburg, once certain conditions and contingencies are met. The EDCs issued the RFP pursuant to Section 83C for Long-Term Contracts for Offshore Wind Energy Generation in June 2017. The EDCs selected an 800 MW project submitted by Vineyard Wind in May 2018, contracts were signed in July 2018 and on July 23, 2018, the EDCs, including Fitchburg, filed two long-term contracts, each for 400 MW of offshore wind energy generation with the MDPU for approval. On April 12, 2019, the MDPU approved the offshore wind energy generation power purchase agreements, including the EDCs’ proposal to sell the energy procured under the contract into the ISO-NE ISO-NE The EDCs issued a second RFP pursuant to Section 83C for Long-Term Contracts for Offshore Wind Energy Generation on May 23, 2019. This solicitation sought to procure the obligation remaining under 83C at the time, an additional 800 MW of offshore wind energy generation. The EDCs selected an 800 MW project submitted by Mayflower Wind Energy LLC and contracts were executed on January 10, 2020. A filing with the MDPU for approval of two long-term contracts, each for 400 MW of offshore wind energy generation, was made on February 10, 2020. On November 5, 2020, the MDPU approved the Offshore Wind Energy Generation power purchase agreements. The MDPU also determined that the EDCs’ request for remuneration equal to 2.75% is reasonable and in the public interest. The Company believes the power purchase obligations under these long-term contracts will have a material effect on the contractual obligations of Fitchburg, once certain conditions and contingencies are met. In accordance with the requirement of Chapter 227 of the Acts of 2018, An Act to Advance Clean Energy, signed August 9, 2018, Massachusetts Department of Energy Resources (MDOER) prepared a report on the necessity, benefits and costs of requiring the EDCs to competitively conduct offshore wind generation RFPs for up to an additional MW. The MDOER filed its report with the Legislature in May, , recommending that, “the EDCs should proceed with additional offshore wind solicitations for up to MW of offshore wind in and and only enter into contracts if found to be cost-effective.” On March , , Fitchburg, along with the other EDCs, filed a petition with the MDPU for approval of a proposed timetable and method of solicitation and execution of long-term contracts for up to an additional MW of off shore wind generation. On May , , the DPU approved the proposed timetable and method for the solicitation, and the RFP was issued on May , . On December , , the EDCs selected a MW portfolio of offshore wind generation that includes a MW project submitted by Vineyard Wind and a MW project submitted by Mayflower Wind. Contract negotiations are expected to be completed by the end of and submitted for approval to the MDPU by the end of . Section 83C of Chapter 169 of the Acts of 2008 was recently amended by the Acts of 2021 to increase the aggregate amount of offshore wind capacity to be procured to 5,600 MW not later than June 30, 2027. After considering there is FERC Transmission Formula Rate Proceedings — The FERC Section 206 proceeding concerning the justness and reasonableness of ISO-New England, Inc. Participating Transmission Owners’ Regional Network Service and Local Network Service formula rates and to develop formula rate protocols for these rates has been resolved. On August 17, 2018 a joint settlement agreement among a number of the parties was filed with the FERC. FERC rejected the settlement agreement on May 22, 2019 and remanded the proceeding to the Chief Administrative Law Judge to resume hearing procedures. On May 24, 2019 the judge appointed a Dispute Resolution Facilitator to aid parties in settlement negotiations. The procedural schedule was suspended September 24, 2019 in order to allow participants to focus on settlement negotiations. On October 24, 2019, the NETOs filed an unopposed motion to suspend the procedural schedule and waiver of answer period indicating that the NETOs, Municipal Pool Transmission Facility Owners and the Commission Trial Staff have reached agreement in principle on the terms of a settlement to resolve all open issues in the proceeding. On June 15, 2020 a settlement was filed. The FERC approved the settlement agreement on December 28, 2020. Pursuant to the terms of the settlement agreement, the negotiated formula rates took effect on January 1, 2022. Fitchburg and Unitil Energy are Participating Transmission Owners, although Unitil Energy does not own transmission plant. To the extent these proceedings result in any changes to the rates being charged, a retroactive reconciliation may be required. The Company does not believe these proceedings will have a material adverse effect on its financial condition or results of operations. Contractual Obligations The following table lists the Company’s known specified gas and electric supply contractual obligations as of December 31, 2021. Payments Due by Period Gas and Electric Supply Contractual Obligations (millions) as of December 31, 2021 Total 2022 2023 2024 2025 2026 2027 & Gas Supply Contracts $ 523.9 $ 58.5 $ 50.6 $ 38.8 $ 37.3 $ 36.9 $ 301.8 Electric Supply Contracts 14.2 1.2 1.2 1.2 1.3 1.3 8.0 Total $ 538.1 $ 59.7 $ 51.8 $ 40.0 $ 38.6 $ 38.2 $ 309.8 The Company and its subsidiaries have material energy supply commitments (see Note 6 Legal Proceedings The Company is involved in legal and administrative proceedings and claims of various types, including those 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 effect on its financial position, operating results or cash flows. Environmental Matters 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 December 31, 2021, has not identified any material losses reasonably likely to be incurred in excess of recorded amounts. However, the Company cannot assure that significant costs and liabilities will not be incurred in the future. It is possible that other developments, such as increasingly stringent federal, state or local environmental laws and regulations could result in increased environmental compliance costs. Based on its current assessment of its environmental responsibilities, existing legal requirements and regulatory policies, the Company does not believe that these environmental costs will have a material adverse effect on the Company’s consolidated financial position or results of operations. Northern Utilities Manufactured Gas Plant Sites mid-1800s mid-1900s. Northern Utilities has worked with the Maine Department of Environmental Protection and New Hampshire Department of Environmental Services (NH DES) to address environmental concerns with these sites. Northern Utilities or others have completed remediation activities at all sites; however, on site monitoring continues at several sites which may result in future remedial actions as directed by the applicable regulatory agency. In July 2019, the NH DES requested that Northern Utilities review modeled expectations for groundwater contaminants against observed data at the Rochester site. In June 2020, the NH DES coupled the submittal of the review to a proposed extension of the gas distribution system by Northern Utilities. Northern Utilities submitted the review in January 2022. In anticipation of the NH DES approval of the work plan, the Company has accrued $0.8 million for estimated costs to complete the remediation at the Rochester site, which is included in Environmental Obligations. 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 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 In August 2021, the Mass DEP issued a Notice of Non-compliance to FGE following a November 2020 audit of the September 2015 Response Action Outcome on the MGP site. Mass DEP directed Fitchburg to further define the extent of MGP site contaminants in the sediment and riverbank of an abutting watercourse. FGE began the investigation in November 2021 with an anticipated completion by June 2022. The Company does not believe this investigation will have a material adverse effect on its financial condition, results of operations or cash flows. 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. Unitil Energy—Kensington Distribution Operations Center The following table sets forth a summary of changes in the Company’s liability for Environmental Obligations for the years-ended December 31, 2021 and 2020. Environmental Obligations ($ millions) December 31, 2021 2020 Total Balance at Beginning of Period $ 2.1 $ 2.7 Additions 0.9 0.2 Less: Payments / Reductions 0.3 0.8 Total Balance at End of Period 2.7 2.1 Less: Current Portion 0.5 0.3 Noncurrent Balance at End of Period $ 2.2 $ 1.8

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2021
Income Taxes	Note 8: Income Taxes Provisions for Federal and , (in millions) 2021 2020 2019 Current Income Tax Provision Federal $ — $ 0.3 $ — State 0.7 0.6 0.3 Total Current Income Taxes $ 0.7 $ 0.9 $ 0.3 Deferred Income Tax Provision Federal $ 7.3 $ 6.5 $ 9.4 State 3.5 2.8 4.1 Total Deferred Income Taxes 10.8 9.3 13.5 Total Income Tax Expense $ 11.5 $ 10.2 $ 13.8 The differences between the Company’s provisions for Income Taxes and the provisions calculated at the statutory federal tax rate, expressed in percentages, are shown in the following table: 2021 2020 2019 Statutory Federal Income Tax Rate 21 % 21 % 21 % Income Tax Effects of: State Income Taxes, net 6 6 6 Utility Plant Differences (3 ) (4 ) (3 ) Other, net — 1 — Effective Income Tax Rate 24 % 24 % 24 % Temporary differences which gave rise to deferred tax assets and liabilities in 2021 and 2020 are shown in the following table: Temporary Differences (in millions) 2021 2020 Deferred Tax Assets Retirement Benefit Obligations $ 34.1 $ 40.7 Net Operating Loss Carryforwards 4.1 — Tax Credit Carryforwards 0.7 0.3 Other, net 1.3 1.3 Total Deferred Tax Assets $ 40.2 $ 42.3 Deferred Tax Liabilities Utility Plant Differences 157.4 $ 143.8 Regulatory Assets & Liabilities 9.4 6.2 Other, net 1.1 1.3 Total Deferred Tax Liabilities 167.9 151.3 Net Deferred Tax Liabilities $ 127.7 $ 109.0 Under the Company’s Tax Sharing Agreement (the Agreement) which was approved upon the formation of Unitil as a public utility holding company, the Company files consolidated Federal and State tax returns and Unitil Corporation and each of its utility operating subsidiaries recognize the results of their operations in its tax returns as if it were a stand-alone taxpayer. The Agreement provides that the Company will account for income taxes in compliance with U.S. GAAP and regulatory accounting principles. The Company has evaluated its tax positions at December 31, 2021 in accordance with the FASB Codification, and has concluded that no adjustment for recognition, de-recognition, events to any tax liabilities or assets as defined by the FASB Codification is required. The Company remains subject to examination by Maine, Massachusetts, and New Hampshire tax authorities for the tax periods ended December 31, 2020; December 31, 2019; and December 31, 2018. Income tax filings for the year ended December 31, 2020 have been filed with the IRS, Massachusetts Department of Revenue, the Maine Revenue Service, and the New Hampshire Department of Revenue Administration. In the Company’s federal tax returns for the year ended December 31, 2020 which were filed with the IRS in October 2021, the Company generated federal Net Operating Loss Carryforward (NOLC) assets of $7.7 million, principally due to tax repairs expense and tax depreciation. As of December 31, 2021, the Company recognized the utilization of approximately In March 2020, the Coronavirus Aid, Relief and Economic Security (CARES) Act was signed into law. The CARES Act included several tax changes as part of its economic package. These changes principally related to expanded Net Operating Loss carryback periods, increases to interest deductibility limitations, and accelerated Alternative Minimum Tax refunds. The Company has evaluated these items and determined that the items do not have a material effect on the Company’s financial statements as of December 31, 2021. Additionally, the CARES Act enacted the Employee Retention Credit (ERC) to incentivize companies to retain employees. The ERC is a 50% credit on employee wages for employees that are retained and cannot perform their job duties at 100% capacity as a result of coronavirus pandemic restrictions. In December 2020, the Consolidated Appropriations Act, 2021 (CAA) was signed into law. The CAA included additional funding through tax credits as part of its economic package for 2021. These changes include the temporary removal of deduction limitations on business meals through December 2022 and additional funding for the ERC with expanded benefits extended through June 30, 2021. The expanded ERC is a 70% credit on employee wages for employees that are retained and cannot perform their job duties at 100% capacity as a result of coronavirus pandemic restrictions. In March 2021, the American Rescue Plan Act of 2021 (ARPA) was signed into law. The ARPA included certain provisions that provide economic relief for the ongoing COVID-19 The Company has evaluated each of the CARES, CAA and ARPA In December 2017, the Tax Cuts and Jobs Act (TCJA), which included a reduction to the corporate federal income tax rate to 21% effective January 1, 2018, was signed into law. In accordance with FASB Codification Topic 740, the Company revalued its Accumulated Deferred Income Taxes (ADIT) at the new 21% tax rate at which the ADIT will be reversed in future periods. The Company recorded a net Regulatory Liability in the amount of $48.9 million at December 31, 2017 as a result of the ADIT revaluation. The Company expects to flow through to customers $47.1 million of excess ADIT in utility base rates. Approximately $1.8 million of excess ADIT was created through reconciling mechanisms at December 31, 2017, which had not been previously collected from customers through utility rates. The Company reconciled these excess ADIT amounts through the specific reconciliation mechanisms in each of those individual reconciling mechanisms which were reviewed by state regulators. In addition to the $48.9 million of net excess ADIT, as of December 31, 2018, there was $2.0 million of remaining excess ADIT created by the recognition of NOLC, and related to the implementation of the new federal tax rate of the TCJA, which had not been previously included in utility rates. The Company recognized the benefit of this excess ADIT in accordance with the regulatory treatment of excess ADIT for each jurisdiction. In 2019, the Company recognized $1.7 million of this amount and the remaining $0.3 million was recognized in 2020. Based on communications received by the Company from its state regulators in rate cases and other regulatory proceedings in the first quarter of 2018 and as prescribed in the TCJA, the recent FERC guidance noted above and IRS normalization rules, the benefit of these protected excess ADIT amounts will be subject to flow back to customers in future utility rates according to the Average Rate Assumption Method (ARAM). ARAM reconciles excess ADIT at the reversal rate of the underlying book/tax temporary timing differences. The Company estimates the ARAM flow back period for protected and unprotected excess ADIT to be between fifteen finalized

Retirement Benefit Plans

Retirement Benefit Plans	12 Months Ended
	Dec. 31, 2021
Retirement Benefits [Abstract]
Retirement Benefit Plans	Note 9: Retirement Benefit Plans The Company sponsors the following retirement benefit plans to provide certain pension and post-retirement benefits for its retirees and current employees as follows: • The Unitil Corporation Retirement Plan (Pension Plan)—The Pension Plan is a defined benefit pension plan. Under the Pension Plan, retirement benefits are based upon an employee’s level of compensation and length of service. Effective January 1, 2010, the Pension Plan was closed to new non-union employees. For union employees, the Pension Plan was closed on various dates between December 31, 2010 and June 1, 2013, depending on the various Collective Bargaining Agreements of each union. • The Unitil Retiree Health and Welfare Benefits Plan (PBOP Plan)—The PBOP Plan provides health care and life insurance benefits to retirees. The Company has established Voluntary Employee Benefit Trusts, into which it funds contributions to the PBOP Plan. • The Unitil Corporation Supplemental Executive Retirement Plan (SERP)—The SERP is a non-qualified retirement plan, with participation limited to executives selected by the Board of Directors. The following table includes the key assumptions used in determining the Company’s benefit plan costs and obligations: 2021 2020 2019 Used to Determine Plan costs for years ended December 31: Discount Rate 2.50 % 3.25 % 4.25 % Rate of Compensation Increase 3.00 % 3.00 % 3.00 % Expected Long-term rate of return on plan assets 7.50 % 7.40 % 7.50 % Health Care Cost Trend Rate Assumed for Next Year 6.60 % 7.00 % 7.00 % Ultimate Health Care Cost Trend Rate 4.50 % 4.50 % 4.50 % Year that Ultimate Health Care Cost Trend Rate is reached 2029 2029 2024 Used to Determine Benefit Obligations at December 31: Discount Rate 2.85 % 2.50 % 3.25 % Rate of Compensation Increase 3.00 % 3.00 % 3.00 % Health Care Cost Trend Rate Assumed for Next Year 6.20 % 6.60 % 7.00 % Ultimate Health Care Cost Trend Rate 4.50 % 4.50 % 4.50 % Year that Ultimate Health Care Cost Trend Rate is reached 2029 2029 2029 The Discount Rate assumptions used in determining retirement plan costs and retirement plan obligations are based on an assessment of current market conditions using high quality corporate bond interest rate indices and pension yield curves. For 2021, a change in the discount rate of 0.25% would have resulted in an increase or decrease of approximately $679,000 in the Net Periodic Benefit Cost (NPBC). The Rate of Compensation Increase assumption used for 2021 was based on the expected long-term increase in compensation costs for personnel covered by the plans. The following table provides the components of the Company’s Retirement plan costs (000’s): Pension Plan PBOP Plan SERP 2021 2020 2019 2021 2020 2019 2021 2020 2019 Service Cost $ 3,472 $ 3,322 $ 3,104 $ 3,034 $ 2,698 $ 2,304 $ 354 $ 283 $ 247 Interest Cost 5,003 5,776 6,484 2,740 3,121 3,426 458 549 567 Expected Return on Plan Assets (9,693 ) (9,019 ) (8,475 ) (2,508 ) (2,063 ) (1,645 ) — — — Prior Service Cost Amortization 301 320 320 1,208 1,210 1,213 56 57 56 Actuarial Loss Amortization 8,089 6,472 4,324 1,045 744 227 1,489 1,036 628 Sub-total 7,172 6,871 5,757 5,519 5,710 5,525 2,357 1,925 1,498 Amounts Capitalized or Deferred (3,384 ) (3,083 ) (2,227 ) (3,136 ) (2,865 ) (2,317 ) (712 ) (579 ) (430 ) NPBC Recognized $ 3,788 $ 3,788 $ 3,530 $ 2,383 $ 2,845 $ 3,208 $ 1,645 $ 1,346 $ 1,068 The Company bases the actuarial determination of pension expense on a market-related valuation of assets, which reduces year-to-year i The following table represents information on the plans’ assets, projected benefit obligations (PBO), and funded status (000’s): Pension Plan PBOP Plan SERP Change in Plan Assets: 2021 2020 2021 2020 2021 2020 Plan Assets at Beginning of Year $ 137,406 $ 125,755 $ 32,847 $ 27,280 $ — $ — Actual Return on Plan Assets 16,989 13,024 3,586 3,739 — — Employer Contributions 4,100 4,665 8,903 4,156 637 654 Participant Contributions — — 220 240 — — Benefits Paid (6,489 ) (6,038 ) (2,905 ) (2,568 ) (637 ) (654 ) Plan Assets at End of Year $ 152,006 $ 137,406 $ 42,651 $ 32,847 $ — $ — Change in PBO: PBO at Beginning of Year $ 206,092 $ 182,135 $ 106,831 $ 95,657 $ 20,225 $ 17,759 Service Cost 3,472 3,322 3,034 2,698 354 283 Interest Cost 5,003 5,776 2,740 3,121 458 549 Participant Contributions — — 220 240 — — Plan Amendments 674 732 — — — — Benefits Paid (6,489 ) (6,038 ) (2,905 ) (2,568 ) (637 ) (654 ) Actuarial (Gain) or Loss (9,334 ) 20,165 2,167 7,683 (2,686 ) 2,288 PBO at End of Year $ 199,418 $ 206,092 $ 112,087 $ 106,831 $ 17,714 $ 20,225 Funded Status: Assets vs PBO $ (47,412 ) $ (68,686 ) $ (69,436 ) $ (73,984 ) $ (17,714 ) $ (20,225 ) The decrease in the PBO for the Pension plan as of Dece m The funded status of the Pension, PBOP and SERP Plans is calculated based on the difference between the benefit obligation and the fair value of plan assets and is recorded on the balance sheets as an asset or a liability. Because the Company recovers the retiree benefit costs from customers through rates, regulatory assets are recorded in lieu of an adjustment to Accumulated Other Comprehensive Income/(Loss). The Company has recorded on its consolidated balance sheets as a liability the underfunded status of its and its subsidiaries’ retirement benefit obligations based on the projected benefit obligation. The Company has recognized Regulatory Assets, net of deferred tax benefits, of $86.4 million and $103.7 million at December 31, 2021 and 2020, respectively, to account for the future collection of these plan obligations in electric and gas rates. The Accumulated Benefit Obligation (ABO) is required to be disclosed for all plans where the ABO is in excess of plan assets. The difference between the PBO and the ABO is that the PBO includes projected compensation increases. The ABO for the Pension Plan was $185.1 million and $189.4 million as of December 31, 2021 and 2020, respectively. The ABO for the SERP was $17.5 million and $16.7 million as of December 31, 2021 and 2020, respectively. For the PBOP Plan, the ABO and PBO are the same. (See Note 1 (Summary of Significant Accounting Policies) for further discussion of SERP funding.) The Company, along with its subsidiaries, expects to continue to make contributions to its Pension Plan in 2022 and future years at minimum required and discretionary funding levels consistent with the amounts recovered in the distribution utilities’ rates for these Pension Plan costs. The following table represents employer contributions, participant contributions and benefit payments ( 000 . Pension Plan PBOP Plan SERP 2021 2020 2019 2021 2020 2019 2021 2020 2019 Employer Contributions $ 4,100 $ 4,665 $ 6,916 $ 8,903 $ 4,156 $ 4,000 $ 637 $ 654 $ 610 Participant Contributions $ — $ — $ — $ 220 $ 240 $ 121 $ — $ — $ — Benefit Payments $ 6,489 $ 6,038 $ 6,877 $ 2,905 $ 2,568 $ 1,758 $ 637 $ 654 $ 610 The following table represents estimated future Estimated Future Benefit Payments Pension PBOP SERP 2022 $ 7,040 $ 3,151 $ 637 2023 8,046 3,448 636 2024 8,497 3,559 635 2025 8,702 3,862 1,090 2026 9,804 4,158 1,144 2027—2031 54,565 23,853 5,583 The Expected Long-Term Rate of Return on Pension Plan assets assumption used by the Company is developed based on input from actuaries and investment managers. The Company’s Expected Long-Term Rate of Return on Pension Plan assets is based on target investment allocation of 56% in common stock equities, 39% in fixed income securities and 5% in real estate securities. The Company’s Expected Long-Term Rate of Return on PBOP Plan assets is based on target investment allocation of 55% in common stock equities and 45% in fixed income securities. The actual investment allocations are shown in the following tables. Pension Plan Target Actual Allocation at 2021 2020 2019 Equity Funds 56 % 57 % 58 % 54 % Debt Funds 39 % 38 % 37 % 36 % Real Estate Fund 5 % 4 % 4 % 9 % Other (1) — 1 % 1 % 1 % Total 100 % 100 % 100 % (1) Represents investments being held in cash equivalents as of December 31, 2021, December 31, 2020 and December 31, 2019 pending payment of benefits. PBOP Plan Target Actual Allocation at 2021 2020 2019 Equity Funds 55 % 56 % 55 % 56 % Debt Funds 45 % 44 % 45 % 44 % Total 100 % 100 % 100 % The combination of these target allocations and expected returns resulted in the overall assumed long-term rate of return of 7.50% for 2021. The Company evaluates the actuarial assumptions, including the expected rate of return, at least annually. The desired investment objective is a long-term rate of return on assets that is approximately 5 – 6% greater than the assumed rate of inflation as measured by the Consumer Price Index. The target rate of return for the Plans has been based upon an analysis of historical returns supplemented with an economic and structural review for each asset class. Following is a description of the valuation methodologies used for assets measured at fair value. There have been no changes in the methodologies used at December 31, 2021 and 2020. Please also see Note 1 (Summary of Significant Accounting Policies) for a discussion of the Company’s fair value accounting policy. Equity, Fixed Income, Index and Asset Allocation Funds These investments are valued based on quoted prices from active markets. These securities are categorized in Level 1 as they are actively traded and no valuation adjustments have been applied. Cash Equivalents These investments are valued at cost, which approximates fair value, and are categorized in Level 1. Real Estate Fund These investments are valued at net asset value per unit based on a combination of market- and income-based models utilizing market discount rates, projected cash flows and the estimated value into perpetuity. In accordance with FASB Codification Topic 820, “Fair Value Measurement”, these investments have not been classified in the fair value hierarchy. The fair value amounts presented in the tables below for the Real Estate Fund are intended to permit reconciliation of the fair value hierarchy to Assets measured at fair value on a recurring basis for the Pension Plan as of December 31, 2021 and 2020 are as follows (000’s): Fair Value Measurements at Reporting Date Using Description Balance as of Quoted Significant Significant 2021 Pension Plan Assets: Mutual Funds: Equity Funds $ 86,356 $ 86,356 $ — $ — Fixed Income Funds 57,883 57,883 — — Total Mutual Funds 144,239 144,239 — — Cash Equivalents 912 912 Total Assets in the Fair Value Hierarchy $ 145,151 $ 145,151 $ — $ — Real Estate Fund–Measured at Net Asset Value 6,855 Total Assets $ 152,006 2020 Pension Plan Assets: Mutual Funds: Equity Funds $ 79,690 $ 79,690 $ — $ — Fixed Income Funds 50,622 50,622 — — Total Mutual Funds 130,312 130,312 — — Cash Equivalents 1,277 1,277 Total Assets in the Fair Value Hierarchy $ 131,589 $ 131,589 $ — $ — Real Estate Fund–Measured at Net Asset Value 5,817 Total Assets $ 137,406 Redemptions of the Real Estate Fund are subject to a sixty-five day notice period and the fund is valued quarterly. There are no unfunded commitments. Assets measured at fair value on a recurring basis for the PBOP Plan as of December 31, 2021 and 2020 are as follows (000’s): Fair Value Measurements at Reporting Date Using Description Balance as of Quoted Significant Significant 2021 PBOP Plan Assets: Mutual Funds: Fixed Income Funds $ 18,882 $ 18,882 $ — $ — Equity Funds 23,769 23,769 — — Total Assets $ 42,651 $ 42,651 $ — $ — 2020 PBOP Plan Assets: Mutual Funds: Fixed Income Funds $ 14,716 $ 14,716 $ — $ — Equity Funds 18,131 18,131 — — Total Assets $ 32,847 $ 32,847 $ — $ — Employee 401(k) Tax Deferred Savings Plan— The Company’s contributions to the 401(k) Plan were $3.3 million, $3.0 million and $2.8 million for the years ended December 31, 2021, 2020 and 2019, respectively.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2021
Accounting Policies [Abstract]
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 capital city areas 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 Maine to the Lewiston-Auburn area and in the greater Fitchburg area of north central Massachusetts. Unitil has three distribution Granite State is an interstate natural gas transmission pipeline company, 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, on May 1, 2003 Unitil Power ceased being the wholesale supplier of Unitil Energy 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. In the period since, Unitil Power continued to flow revenues and expenses from remaining contracts to Unitil Energy under the Amended Unitil System Agreement. The last of those contracts expired October 31, 2020, and the Company no longer has material revenues or expenses associated with those contracts. 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
Divestiture of Non-Regulated Business Subsidiary	Divestiture of Non-Regulated Business Subsidiary — million on this divestiture is included in Other Income (Expense), Net on the Consolidated Statements of Earnings for the year-ended December 31, 2019, while the income taxes associated with this transaction of million are included in the Provision For Income Taxes.
Principles of Consolidation	Principles of Consolidation —
Use of Estimates	Use of Estimates —
Fair Value	Fair Value — Level 1— Inputs are quoted prices (unadjusted) in active markets for identical assets or liabilities that the reporting entity has the ability to access at the measurement date. Level 2— Valuations based on quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly. Level 3— Prices or valuations that require inputs that are both significant to the fair value measurement and unobservable. To the extent valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair value requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized in Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company’s own assumptions are set to reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including during periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may be reduced for many instruments. This condition could cause an instrument to be reclassified from Level 1 to Level 2 or from Level 2 to Level 3. There have been no changes in the valuation techniques used during the current period.
Utility Revenue Recognition	Utility Revenue Recognition — Billed and unbilled revenue is recorded when service is rendered or energy is delivered to customers. However, the determination of energy sales to individual customers is based on the reading of their meters, which occurs on a systematic basis throughout the month. At the end of each calendar month, amounts of energy delivered to customers since the date of the last meter reading are estimated and the corresponding unbilled revenues are calculated. These unbilled revenues are estimated each month based on estimated customer usage by class and applicable customer rates, taking into account current and historical weather data, assumptions pertaining to metering patterns, billing cycle statistics, and other estimates and assumptions, and are then reversed in the following month when billed to customers. A majority of the Company’s revenue from contracts with customers continues to be recognized on a monthly basis based on applicable tariffs and customer monthly consumption. Such revenue is recognized using the invoice practical expedient which allows an entity to recognize revenue in the amount that directly corresponds to the value transferred to the customer. The Company’s billed and unbilled rev e In the following tables, revenue is classified by the types of goods/services rendered and market/customer type. Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 135.1 $ 83.9 $ 219.0 Commercial & Industrial 103.3 124.1 227.4 Other 10.1 9.6 19.7 Total Billed and Unbilled Revenue 248.5 217.6 466.1 Rate Adjustment Mechanism Revenue — 7.2 7.2 Total Electric and Gas Operating Revenues $ 248.5 $ 224.8 $ 473.3 Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 128.7 $ 73.1 $ 201.8 Commercial & Industrial 91.4 104.5 195.9 Other 6.6 7.6 14.2 Total Billed and Unbilled Revenue 226.7 185.2 411.9 Rate Adjustment Mechanism Revenue 0.5 6.2 6.7 Total Electric and Gas Operating Revenues $ 227.2 $ 191.4 $ 418.6 Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 121.5 $ 81.4 $ 202.9 Commercial & Industrial 93.8 120.1 213.9 Other 7.8 10.6 18.4 Total Billed and Unbilled Revenue 223.1 212.1 435.2 Rate Adjustment Mechanism Revenue 10.8 (8.7 ) 2.1 Total Electric and Gas Operating Revenues $ 233.9 $ 203.4 $ 437.3 Fitchburg is subject to revenue decoupling. Revenue decoupling is the term given to the elimination of the dependency of a utility’s distribution revenue on the volume of electricity or natural gas sales. The difference between distribution revenue amounts billed to customers and the targeted revenue decoupling amounts is recorded as an increase or a decrease in the current portion of Accrued Revenue, which forms the basis for resetting rates for future cash recoveries from, or credits to, customers. These revenue decoupling targets may be adjusted as a result of rate cases that the Company files with the Massachusetts Department of Public Utilities (MDPU). The Company estimates that revenue decoupling applies to approximately 27% and 11% of Unitil’s total annual electric and natural gas sales volumes, respectively. The Company bills its customers for sales tax in Massachusetts and Maine. These taxes are remitted to the appropriate departments of revenue in each state and are excluded from revenues on the Company’s Consolidated Statements of Earnings.
Other Operating Revenue - Non-regulated	Other Operating Revenue—Non-regulated —
Depreciation and Amortization	Depreciation and Amortization —
Stock-based Employee Compensation	Stock-based Employee Compensation —
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 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.
Dividends	Dividends y annualized dividend rates of $1.50 and $1.48 per common share, respectively. At its January 2022 meeting, the Unitil Corporation Board of Directors declared a quarterly dividend on the Company’s common stock of $0.39 per share, an increase of $0.01 per share on a quarterly basis, resulting in an increase in the effective annualized dividend rate to $1.56 per share from $1.52 per share.
Cash and Cash Equivalents	Cash and Cash Equivalents (ISO-NE) ISO-NE. 2-1/2 ISO-NE
Financial Instruments	Financial Instruments 2016-13,
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts — Accounts Receivable, Net includes $3.1 million and $3.1 million of the Allowance for Doubtful Accounts at December 31, 2021 and December 31, 2020, respectively. Unbilled Revenues, net (a component of Accrued Revenue) includes $0.2 million and $0.2 million of the Allowance for Doubtful Accounts at December 31, 2021 and December 31, 2020, respectively.
Accrued Revenue	Accrued Revenue— Accrued Revenue (millions) December 31, 2021 2020 Regulatory Assets—Current $ 47.4 $ 37.3 Unbilled Revenues 13.8 13.6 Total Accrued Revenue $ 61.2 $ 50.9
Exchange Gas Receivable	Exchange Gas Receivable — through March. The exchange and storage gas volumes are recorded at weighted average cost. The following table shows the components of Exchange Gas Receivable as of December 31, 2021 and 2020. Exchange Gas Receivable (millions) December 31, 2021 2020 Northern Utilities $ 6.7 $ 4.4 Fitchburg 0.7 0.5 Total Exchange Gas Receivable $ 7.4 $ 4.9
Gas Inventory	Gas Inventory Gas Inventory (millions) December 31, 2021 2020 Natural Gas $ 0.5 $ 0.2 Propane 0.4 0.3 Liquefied Natural Gas & Other 0.1 0.1 Total Gas Inventory $ 1.0 $ 0.6 The Company also has an inventory of Materials and Supplies in the amounts of $8.6 million and $8.5 million as of December 31, 2021 and December 31, 2020, respectively. These amounts are recorded at weighted average cost.
Utility Plant	Utility Plant Cost of additions consists of The costs of current repairs and minor replacements are charged to appropriate operating expense accounts. The original cost of utility plant retired or otherwise disposed of is charged to the accumulated provision for depreciation. The Company includes in its mass asset depreciation rates, which are periodically reviewed as part of its ratemaking proceedings, cost of removal amounts to provide for future negative salvage value. At December 31, 2021 and 2020, the Company has recorded cost of removal amounts of $107.5 million and $105.2 million, respectively, that have been collected in depreciation rates but have not yet been expended, and which represent regulatory liabilities. These amounts are recorded on the Consolidated Balance Sh e
Regulatory Accounting	Regulatory Accounting — following table. Regulatory Assets consist of the following (millions) December 31, 2021 2020 Retirement Benefits $ 86.4 $ 103.7 Energy Supply & Other Rate Adjustment Mechanisms 44.1 34.1 Deferred Storm Charges 3.3 4.1 Environmental 4.6 5.2 Income Taxes 2.6 3.4 Other Deferred Charges 15.3 14.2 Total Regulatory Assets 156.3 164.7 Less: Current Portion of Regulatory Assets (1) 47.4 37.3 Regulatory Assets—noncurrent $ 108.9 $ 127.4 (1) Reflects amounts included in the Accrued Revenue on the Company’s Consolidated Balance Sheets. Regulatory Liabilities consist of the following (millions) December 31, 2021 2020 Rate Adjustment Mechanisms $ 7.7 $ 4.1 Income Taxes 44.3 45.5 Other 0.1 0.2 Total Regulatory Liabilities 52.1 49.8 Less: Current Portion of Regulatory Liabilities 9.5 5.5 Regulatory Liabilities—noncurrent $ 42.6 $ 44.3 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 December 31, 2021 are $8.5 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 effect 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 Regul a 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.
Leases	Leases non-lease v 4
Derivatives	Derivatives — The Company had no derivative assets or liabilities recorded on its Consolidated Balance Sheets as of December 31, 2021 and December 31, 2020. There were no losses / (gains) recognized in Regulatory Assets / Liabilities for the years ended December 31, 2021 and 2020. There were no losses / (gains) reclassified into the Consolidated Statements of Earnings for the years ended December 31, 2021, 2020 and 2019. Fitchburg has entered into power purchase agreements for which contingencies exist (see “Fitchburg – Massachusetts RFP’s” section of Note 7 (Commitments and Contingencies). Until these contingencies are satisfied, these contracts will not qualify for derivative accounting. The Company believes that the power purchase obligations under these long-term contracts will have a material effect on the contractual obligations of Fitchburg.
Investments in Marketable Securities	Investments in Marketable Securities — At December 31, 2021 and 2020, the fair value of the Company’s investments in these trading securities, which are recorded on the Consolidated Balance Sheets in Other Assets, were $5.7 million and $5.7 million, respectively, as shown in the following table. Fair Value of Marketable Securities (millions) December 31, 2021 2020 Money Market Funds $ 5.7 $ 5.7 Total Marketable Securities $ 5.7 $ 5.7 The Company also sponsors the Unitil Corporation Deferred Compensation Plan (the DC Plan). The DC Plan is a non-qualified tax-deferred participants to defer up to 85% of base salary, and up to 85% of any cash incentive for retirement. The Company may also elect to make discretionary contributions on behalf of any participant in an amount determined by the Company’s Board of Directors. A trust has been established to invest the funds associated with the DC Plan. At December 31, 2021 and 2020, the fair value of the Company’s investments in these trading securities related to the DC Plan, which are recorded on the Consolidated Balance Sheets in Other Assets, were $ million and $ million, respectively. 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 (Income) Expense, Net. Fair Value of Marketable Securities (millions) December 31, 2021 2020 Equity Funds $ 0.2 $ 0.2 Money Market Funds 0.4 0.3 Total Marketable Securities $ 0.6 $ 0.5
Energy Supply Obligations	Energy Supply Obligations December 31, Energy Supply Obligations consist of the following: (millions) 2021 2020 Renewable Energy Portfolio Standards $ 7.8 $ 5.7 Exchange Gas Obligation 6.7 4.4 Power Supply Contract Divestitures — 0.3 Total Energy Supply Obligations $ 14.5 $ 10.4 Renewable Energy Portfolio Standards Fitchburg has e n Exchange Gas Obligation — Power Supply Contract Divestitures— o
Retirement Benefit Obligations	Retirement Benefit Obligations non-union non-qualified The Company records on its balance sheets as an asset or liability the overfunded or underfunded status of its retirement benefit obligations (RBO) based on the projected benefit obligations. The Company has recognized a corresponding Regulatory Asset, reflecting ultimate recovery from customers through rates. The regulatory asset (or regulatory liability) is amortized as the actuarial gains and losses and prior service cost are amortized to net periodic benefit cost for the Pension and PBOP plans. All amounts are remeasured annually. (See Note 9 Retirement Benefit Plans).
Commitments and Contingencies	Commitments and Contingencies 7
Environmental Matters	Environmental Matters 7 o
Subsequent Events	Subsequent Events

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2021
Components of Gas and Electric Operating Revenue	In the following tables, revenue is classified by the types of goods/services rendered and market/customer type. Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 135.1 $ 83.9 $ 219.0 Commercial & Industrial 103.3 124.1 227.4 Other 10.1 9.6 19.7 Total Billed and Unbilled Revenue 248.5 217.6 466.1 Rate Adjustment Mechanism Revenue — 7.2 7.2 Total Electric and Gas Operating Revenues $ 248.5 $ 224.8 $ 473.3 Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 128.7 $ 73.1 $ 201.8 Commercial & Industrial 91.4 104.5 195.9 Other 6.6 7.6 14.2 Total Billed and Unbilled Revenue 226.7 185.2 411.9 Rate Adjustment Mechanism Revenue 0.5 6.2 6.7 Total Electric and Gas Operating Revenues $ 227.2 $ 191.4 $ 418.6 Twelve Months Ended Electric and Gas Operating Revenues (millions): Electric Gas Total Billed and Unbilled Revenue: Residential $ 121.5 $ 81.4 $ 202.9 Commercial & Industrial 93.8 120.1 213.9 Other 7.8 10.6 18.4 Total Billed and Unbilled Revenue 223.1 212.1 435.2 Rate Adjustment Mechanism Revenue 10.8 (8.7 ) 2.1 Total Electric and Gas Operating Revenues $ 233.9 $ 203.4 $ 437.3
Components of Accrued Revenue	The following table shows the components of Accrued Revenue as of December 31, 2021 and 2020. Accrued Revenue (millions) December 31, 2021 2020 Regulatory Assets—Current $ 47.4 $ 37.3 Unbilled Revenues 13.8 13.6 Total Accrued Revenue $ 61.2 $ 50.9
Components of Exchange Gas Receivable	The following table shows the components of Exchange Gas Receivable as of December 31, 2021 and 2020. Exchange Gas Receivable (millions) December 31, 2021 2020 Northern Utilities $ 6.7 $ 4.4 Fitchburg 0.7 0.5 Total Exchange Gas Receivable $ 7.4 $ 4.9
Components of Gas Inventory	The following table shows the components of Gas Inventory as of December 31, 2021 and 2020. Gas Inventory (millions) December 31, 2021 2020 Natural Gas $ 0.5 $ 0.2 Propane 0.4 0.3 Liquefied Natural Gas & Other 0.1 0.1 Total Gas Inventory $ 1.0 $ 0.6
Regulatory Assets	Regulatory Assets consist of the following (millions) December 31, 2021 2020 Retirement Benefits $ 86.4 $ 103.7 Energy Supply & Other Rate Adjustment Mechanisms 44.1 34.1 Deferred Storm Charges 3.3 4.1 Environmental 4.6 5.2 Income Taxes 2.6 3.4 Other Deferred Charges 15.3 14.2 Total Regulatory Assets 156.3 164.7 Less: Current Portion of Regulatory Assets (1) 47.4 37.3 Regulatory Assets—noncurrent $ 108.9 $ 127.4 (1) Reflects amounts included in the Accrued Revenue on the Company’s Consolidated Balance Sheets.
Regulatory Liabilities	Regulatory Liabilities consist of the following (millions) December 31, 2021 2020 Rate Adjustment Mechanisms $ 7.7 $ 4.1 Income Taxes 44.3 45.5 Other 0.1 0.2 Total Regulatory Liabilities 52.1 49.8 Less: Current Portion of Regulatory Liabilities 9.5 5.5 Regulatory Liabilities—noncurrent $ 42.6 $ 44.3
Fair Value of Marketable Securities	Fair Value of Marketable Securities (millions) December 31, 2021 2020 Money Market Funds $ 5.7 $ 5.7 Total Marketable Securities $ 5.7 $ 5.7
Components of Energy Supply Obligations	December 31, Energy Supply Obligations consist of the following: (millions) 2021 2020 Renewable Energy Portfolio Standards $ 7.8 $ 5.7 Exchange Gas Obligation 6.7 4.4 Power Supply Contract Divestitures — 0.3 Total Energy Supply Obligations $ 14.5 $ 10.4
Deferred Compensation Plan [Member]
Components of Energy Supply Obligations	Fair Value of Marketable Securities (millions) December 31, 2021 2020 Equity Funds $ 0.2 $ 0.2 Money Market Funds 0.4 0.3 Total Marketable Securities $ 0.6 $ 0.5

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2021
Significant Segment Financial Data	The following tables provide significant segment financial data for the years ended December 31, 2021, 2020 and 2019 (millions) : Year Ended December 31, 2021 Electric Gas Non- Other Total Revenues: Billed and Unbilled Revenue $ 248.5 $ 217.6 $ — $ — $ 466.1 Rate Adjustment Mechanism Revenue — 7.2 — — 7.2 Total Operating Revenues 248.5 224.8 — — 473.3 Interest Income 0.8 0.5 — 0.3 1.6 Interest Expense 9.0 15.3 — 2.9 27.2 Depreciation & Amortization Expense 25.9 32.6 — 1.0 59.5 Income Tax Expense (Benefit) 4.5 7.7 (0.1 ) (0.6 ) 11.5 Segment Profit (Loss) 14.0 23.2 0.1 (1.2 ) 36.1 Segment Assets 584.0 935.9 — 20.4 1,540.3 Capital Expenditures 38.1 75.8 — 1.1 115.0 Year Ended December 31, 2020 Revenues: Billed and Unbilled Revenue $ 226.7 $ 185.2 $ — $ — $ 411.9 Rate Adjustment Mechanism Revenue 0.5 6.2 — — 6.7 Total Operating Revenues 227.2 191.4 — — 418.6 Interest Income 1.1 1.1 — 0.4 2.6 Interest Expense 8.7 14.2 — 3.5 26.4 Depreciation & Amortization Expense 23.8 29.8 — 0.9 54.5 Income Tax Expense (Benefit) 4.7 7.3 — (1.8 ) 10.2 Segment Profit 12.9 19.3 — — 32.2 Segment Assets 571.8 886.3 — 19.8 1,477.9 Capital Expenditures 45.5 71.1 — 6.0 122.6 Year Ended December 31, 2019 Revenues: Billed and Unbilled Revenue $ 223.1 $ 212.1 $ — $ — $ 435.2 Rate Adjustment Mechanism Revenue 10.8 (8.7 ) — — 2.1 Other Operating Revenue—Non-Regulated — — 0.9 — 0.9 Total Operating Revenues 233.9 203.4 0.9 — 438.2 Interest Income 0.9 1.2 0.2 0.6 2.9 Interest Expense 9.4 14.4 — 2.8 26.6 Depreciation & Amortization Expense 22.6 28.5 — 0.9 52.0 Income Tax Expense (Benefit) 4.2 7.2 3.8 (1.4 ) 13.8 Segment Profit 11.5 19.1 10.2 3.4 44.2 Segment Assets 529.3 823.3 0.3 17.9 1,370.8 Capital Expenditures 39.6 74.0 — 5.6 119.2

Allowance for Doubtful Accoun_2

Allowance for Doubtful Accounts (Tables)	12 Months Ended
	Dec. 31, 2021
Allowance For Doubtful Accounts [Abstract]
Allowance for Doubtful Accounts	The following table shows the balances and activity in the Company’s Allowance for Doubtful Accounts for 2021, 2020 and 2019 (millions): ALLOWANCE FOR DOUBTFUL ACCOUNTS Balance at Provision Recoveries Accounts Regulatory Deferrals* Balance at Year Ended December 31, 2021 Electric $ 1.6 $ 3.3 $ 0.4 $ 3.4 $ 0.1 $ 2.0 Gas 1.7 2.3 0.4 3.1 — 1.3 Other — — — — — — $ 3.3 $ 5.6 $ 0.8 $ 6.5 $ 0.1 $ 3.3 Year Ended December 31, 2020 Electric $ 0.6 $ 2.9 $ 0.3 $ 2.6 $ 0.4 $ 1.6 Gas 0.4 2.6 0.3 1.8 0.2 1.7 Other — — — — — — $ 1.0 $ 5.5 $ 0.6 $ 4.4 $ 0.6 $ 3.3 Year Ended December 31, 2019 Electric $ 0.5 $ 3.0 $ 0.3 $ 3.2 $ — $ 0.6 Gas 0.8 1.9 0.5 2.8 — 0.4 Other — — — — — — $ 1.3 $ 4.9 $ 0.8 $ 6.0 $ — $ 1.0

Debt and Financing Arrangemen_2

Debt and Financing Arrangements (Tables)	12 Months Ended
	Dec. 31, 2021
Details on Long Term Debt	Details on long-term debt at December 31, 2021 and 2020 are shown below: Long-Term Debt (millions) December 31, 2021 2020 Unitil Corporation: 6.33% Senior Notes, Due May 1, 2022 $ — $ 15.0 3.70% Senior Notes, Due August 1, 2026 30.0 30.0 3.43% Senior Notes, Due December 18, 2029 30.0 30.0 Unitil Energy First Mortgage Bonds: 8.49% Senior Secured Notes, Due October 14, 2024 1.5 3.0 6.96% Senior Secured Notes, Due September 1, 2028 14.0 16.0 8.00% Senior Secured Notes, Due May 1, 2031 15.0 15.0 6.32% Senior Secured Notes, Due September 15, 2036 15.0 15.0 3.58% Senior Secured Notes, Due September 15, 2040 27.5 27.5 4.18% Senior Secured Notes, Due November 30, 2048 30.0 30.0 Fitchburg: 6.75% Senior Notes, Due November 30, 2023 — 1.9 6.79% Senior Notes, Due October 15, 2025 6.0 10.0 3.52% Senior Notes, Due November 1, 2027 10.0 10.0 7.37% Senior Notes, Due January 15, 2029 9.6 10.8 5.90% Senior Notes, Due December 15, 2030 15.0 15.0 7.98% Senior Notes, Due June 1, 2031 14.0 14.0 3.78% Senior Notes, Due September 15, 2040 27.5 27.5 4.32% Senior Notes, Due November 1, 2047 15.0 15.0 Northern Utilities: 3.52% Senior Notes, Due November 1, 2027 20.0 20.0 7.72% Senior Notes, Due December 3, 2038 50.0 50.0 3.78% Senior Notes, Due September 15, 2040 40.0 40.0 4.42% Senior Notes, Due October 15, 2044 50.0 50.0 4.32% Senior Notes, Due November 1, 2047 30.0 30.0 4.04% Senior Notes, Due September 12, 2049 40.0 40.0 Granite State: 3.72% Senior Notes, Due November 1, 2027 15.0 15.0 Unitil Realty Corp.: 2.64% Senior Secured Notes, Due December 18, 2030 4.5 4.7 Total Long-Term Debt 509.6 535.4 Less: Unamortized Debt Issuance Costs 3.6 3.8 Total Long-Term Debt, net of Unamortized Debt Issuance Costs 506.0 531.6 Less: Current Portion (1) 8.2 8.5 Total Long-Term Debt, Less Current Portion $ 497.8 $ 523.1 (1) The Current Portion of Long-Term Debt includes sinking fund payments.
Fair Value of Long Term Debt	Estimated Fair Value of Long-Term Debt (millions) December 31, 2021 2020 Estimated Fair Value of Long-Term Debt $ 584.9 $ 633.1
Summary of Interest Expense and Interest Income	A summary of interest expense and interest income is provided in the following table Interest Expense, Net (millions) 2021 2020 2019 Interest Expense Long-Term Debt $ 26.0 $ 24.8 $ 22.9 Short-Term Debt 0.8 1.4 3.0 Regulatory Liabilities 0.4 0.2 0.7 Subtotal Interest Expense 27.2 26.4 26.6 Interest Income Regulatory Assets (0.5 ) (0.8 ) (0.8 ) AFUDC (1) (1.1 ) (1.8 ) (2.1 ) Subtotal Interest Income (1.6 ) (2.6 ) (2.9 ) Total Interest Expense, Net $ 25.6 $ 23.8 $ 23.7 (1) AFUDC—Allowance for Funds Used During Construction
Borrowing Limits Amounts Outstanding and Amounts Available under Credit Facility	The following table details the borrowing limits, amounts outstanding and amounts available under the revolving Credit Facility as of December 31, 2021 and December 31, 2020: Revolving Credit Facility (millions) December 31, 2021 2020 Limit $ 120.0 $ 120.0 Short-Term Borrowings Outstanding $ 64.1 $ 54.7 Letters of Credit Outstanding $ — $ 0.1 Available $ 55.9 $ 65.2
Summary of Company's Contractual Obligations for Log-term Debt	The following table lists the Company’s contractual obligations for long-term debt as of December 31, 2021. Payments Due by Period Long-Term Debt Contractual Obligations (millions) as of December 31, 2021 Total 2022 2023 2024 2025 2026 2027 & Long-Term Debt $ 509.6 $ 8.4 $ 6.9 $ 6.9 $ 5.0 $ 38.0 $ 444.4 Interest on Long-Term Debt 360.5 24.5 23.9 23.4 22.9 22.6 243.2 Total $ 870.1 $ 32.9 $ 30.8 $ 30.3 $ 27.9 $ 60.6 $ 687.6
Classification of the Company Lease Obligations	The balance sheet classification of the Company’s lease obligations was as follows: December 31, Lease Obligations (millions) 2021 2020 Operating Lease Obligations: Other Current Liabilities (current portion) $ 1.6 $ 1.5 Other Noncurrent Liabilities (long-term portion) 3.1 3.7 Total Operating Lease Obligations 4.7 5.2 Capital Lease Obligations: Other Current Liabilities (current portion) 0.1 0.2 Other Noncurrent Liabilities (long-term portion) 0.2 0.2 Total Capital Lease Obligations 0.3 0.4 Total Lease Obligations $ 5.0 $ 5.6
Future Operating Lease Payment Obligations and Future Minimum Lease Payments under Capital Leases	The following table is a schedule of future operating lease payment obligations and future minimum lease payments under capital leases as of December 31, 2021. The payments for operating leases consist of $1.6 million of current operating lease obligations, which are included in Other Current Liabilities and $3.1 million of noncurrent operating lease obligations, which are included in Other Noncurrent Liabilities, on the Company’s Consolidated Balance Sheets as of December 31, 2021. The payments for capital leases consist of $0.1 million of current Capital Lease Obligations Lease Payments ($000’s) Year Ending December 31, Operating Capital 2022 $ 1,695 $ 150 2023 1,399 107 2024 1,069 52 2025 503 19 2026 199 — 2027-2031 121 — Total Payments 4,986 328 Less: Interest 316 12 Amount of Lease Obligations Recorded on Consolidated Balance Sheets $ 4,670 $ 316

Equity (Tables)

Equity (Tables)	12 Months Ended
	Dec. 31, 2021
Table Text Block Supplement [Abstract]
Restricted Shares Issued in Conjunction with Stock Plan	Restricted Shares issued for 2019 – 2021 in conjunction with the Stock Plan are presented in the following table: Issuance Date Shares Aggregate 1/29/19 33,150 $1.6 1/28/20 28,630 $1.8 7/28/20 3,000 $0.1 1/26/21 23,140 $0.9
Restricted Stock Units Issued	The equity portion of Restricted Stock Units activity during 2021 and 2020 in conjunction with the Stock Plan are presented in the following table: Restricted Stock Units (Equity Portion) 2021 2020 Units Weighted Units Weighted Beginning Restricted Stock Units 43,192 $ 41.34 70,364 $ 41.20 Restricted Stock Units Granted 4,519 $ 43.35 3,743 $ 39.26 Dividend Equivalents Earned 1,471 $ 46.34 1,507 $ 47.34 Restricted Stock Units Settled — $ — (32,422 ) $ 41.09 Ending Restricted Stock Units 49,182 $ 41.67 43,192 $ 41.34
Reconciliation of Basic and Diluted Earnings Per Share	The following table reconciles basic and diluted earnings per share (EPS). (Millions except shares and per share data) 2021 2020 2019 Earnings Available to Common Shareholders $ 36.1 $ 32.2 $ 44.2 Weighted Average Common Shares Outstanding—Basic (000’s) 15,373 14,951 14,894 Plus: Diluted Effect of Incremental Shares (000’s) 3 1 6 Weighted Average Common Shares Outstanding—Diluted (000’s) 15,376 14,952 14,900 Earnings per Share—Basic and Diluted $ 2.35 $ 2.15 $ 2.97
Weighted Average Non Vested Restricted Shares Excluded from Computation of Earnings Per Share	The following table shows the number of weighted average non-vested 2021 2020 2019 Weighted Average Non-Vested 23,636 42,813 —

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Gas And Electric Supply Contractual Obligations	The following table lists the Company’s known specified gas and electric supply contractual obligations as of December 31, 2021. Payments Due by Period Gas and Electric Supply Contractual Obligations (millions) as of December 31, 2021 Total 2022 2023 2024 2025 2026 2027 & Gas Supply Contracts $ 523.9 $ 58.5 $ 50.6 $ 38.8 $ 37.3 $ 36.9 $ 301.8 Electric Supply Contracts 14.2 1.2 1.2 1.2 1.3 1.3 8.0 Total $ 538.1 $ 59.7 $ 51.8 $ 40.0 $ 38.6 $ 38.2 $ 309.8
Environmental Obligations Recognized by Company	The following table sets forth a summary of changes in the Company’s liability for Environmental Obligations for the years-ended December 31, 2021 and 2020. Environmental Obligations ($ millions) December 31, 2021 2020 Total Balance at Beginning of Period $ 2.1 $ 2.7 Additions 0.9 0.2 Less: Payments / Reductions 0.3 0.8 Total Balance at End of Period 2.7 2.1 Less: Current Portion 0.5 0.3 Noncurrent Balance at End of Period $ 2.2 $ 1.8

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2021
Income Tax Disclosure [Abstract]
Provisions for Federal and State Income Taxes	Provisions for Federal and , (in millions) 2021 2020 2019 Current Income Tax Provision Federal $ — $ 0.3 $ — State 0.7 0.6 0.3 Total Current Income Taxes $ 0.7 $ 0.9 $ 0.3 Deferred Income Tax Provision Federal $ 7.3 $ 6.5 $ 9.4 State 3.5 2.8 4.1 Total Deferred Income Taxes 10.8 9.3 13.5 Total Income Tax Expense $ 11.5 $ 10.2 $ 13.8
Differences Between Provisions for Income Taxes and Provisions Calculated at Statutory Federal Tax Rate	The differences between the Company’s provisions for Income Taxes and the provisions calculated at the statutory federal tax rate, expressed in percentages, are shown in the following table: 2021 2020 2019 Statutory Federal Income Tax Rate 21 % 21 % 21 % Income Tax Effects of: State Income Taxes, net 6 6 6 Utility Plant Differences (3 ) (4 ) (3 ) Other, net — 1 — Effective Income Tax Rate 24 % 24 % 24 %
Deferred Tax Assets and Liabilities	Temporary differences which gave rise to deferred tax assets and liabilities in 2021 and 2020 are shown in the following table: Temporary Differences (in millions) 2021 2020 Deferred Tax Assets Retirement Benefit Obligations $ 34.1 $ 40.7 Net Operating Loss Carryforwards 4.1 — Tax Credit Carryforwards 0.7 0.3 Other, net 1.3 1.3 Total Deferred Tax Assets $ 40.2 $ 42.3 Deferred Tax Liabilities Utility Plant Differences 157.4 $ 143.8 Regulatory Assets & Liabilities 9.4 6.2 Other, net 1.1 1.3 Total Deferred Tax Liabilities 167.9 151.3 Net Deferred Tax Liabilities $ 127.7 $ 109.0

Retirement Benefit Plans (Table

Retirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2021
Key Weighted Average Assumptions Used in Determining Benefit Plan Costs and Obligations	The following table includes the key assumptions used in determining the Company’s benefit plan costs and obligations: 2021 2020 2019 Used to Determine Plan costs for years ended December 31: Discount Rate 2.50 % 3.25 % 4.25 % Rate of Compensation Increase 3.00 % 3.00 % 3.00 % Expected Long-term rate of return on plan assets 7.50 % 7.40 % 7.50 % Health Care Cost Trend Rate Assumed for Next Year 6.60 % 7.00 % 7.00 % Ultimate Health Care Cost Trend Rate 4.50 % 4.50 % 4.50 % Year that Ultimate Health Care Cost Trend Rate is reached 2029 2029 2024 Used to Determine Benefit Obligations at December 31: Discount Rate 2.85 % 2.50 % 3.25 % Rate of Compensation Increase 3.00 % 3.00 % 3.00 % Health Care Cost Trend Rate Assumed for Next Year 6.20 % 6.60 % 7.00 % Ultimate Health Care Cost Trend Rate 4.50 % 4.50 % 4.50 % Year that Ultimate Health Care Cost Trend Rate is reached 2029 2029 2029
Components of Retirement Plan Costs	The following table provides the components of the Company’s Retirement plan costs (000’s): Pension Plan PBOP Plan SERP 2021 2020 2019 2021 2020 2019 2021 2020 2019 Service Cost $ 3,472 $ 3,322 $ 3,104 $ 3,034 $ 2,698 $ 2,304 $ 354 $ 283 $ 247 Interest Cost 5,003 5,776 6,484 2,740 3,121 3,426 458 549 567 Expected Return on Plan Assets (9,693 ) (9,019 ) (8,475 ) (2,508 ) (2,063 ) (1,645 ) — — — Prior Service Cost Amortization 301 320 320 1,208 1,210 1,213 56 57 56 Actuarial Loss Amortization 8,089 6,472 4,324 1,045 744 227 1,489 1,036 628 Sub-total 7,172 6,871 5,757 5,519 5,710 5,525 2,357 1,925 1,498 Amounts Capitalized or Deferred (3,384 ) (3,083 ) (2,227 ) (3,136 ) (2,865 ) (2,317 ) (712 ) (579 ) (430 ) NPBC Recognized $ 3,788 $ 3,788 $ 3,530 $ 2,383 $ 2,845 $ 3,208 $ 1,645 $ 1,346 $ 1,068
Plans' Assets, Projected Benefit Obligations (PBO), and Funded Status	The following table represents information on the plans’ assets, projected benefit obligations (PBO), and funded status (000’s): Pension Plan PBOP Plan SERP Change in Plan Assets: 2021 2020 2021 2020 2021 2020 Plan Assets at Beginning of Year $ 137,406 $ 125,755 $ 32,847 $ 27,280 $ — $ — Actual Return on Plan Assets 16,989 13,024 3,586 3,739 — — Employer Contributions 4,100 4,665 8,903 4,156 637 654 Participant Contributions — — 220 240 — — Benefits Paid (6,489 ) (6,038 ) (2,905 ) (2,568 ) (637 ) (654 ) Plan Assets at End of Year $ 152,006 $ 137,406 $ 42,651 $ 32,847 $ — $ — Change in PBO: PBO at Beginning of Year $ 206,092 $ 182,135 $ 106,831 $ 95,657 $ 20,225 $ 17,759 Service Cost 3,472 3,322 3,034 2,698 354 283 Interest Cost 5,003 5,776 2,740 3,121 458 549 Participant Contributions — — 220 240 — — Plan Amendments 674 732 — — — — Benefits Paid (6,489 ) (6,038 ) (2,905 ) (2,568 ) (637 ) (654 ) Actuarial (Gain) or Loss (9,334 ) 20,165 2,167 7,683 (2,686 ) 2,288 PBO at End of Year $ 199,418 $ 206,092 $ 112,087 $ 106,831 $ 17,714 $ 20,225 Funded Status: Assets vs PBO $ (47,412 ) $ (68,686 ) $ (69,436 ) $ (73,984 ) $ (17,714 ) $ (20,225 )
Employer Contributions, Participant Contributions and Benefit Payments	The following table represents employer contributions, participant contributions and benefit payments ( 000 . Pension Plan PBOP Plan SERP 2021 2020 2019 2021 2020 2019 2021 2020 2019 Employer Contributions $ 4,100 $ 4,665 $ 6,916 $ 8,903 $ 4,156 $ 4,000 $ 637 $ 654 $ 610 Participant Contributions $ — $ — $ — $ 220 $ 240 $ 121 $ — $ — $ — Benefit Payments $ 6,489 $ 6,038 $ 6,877 $ 2,905 $ 2,568 $ 1,758 $ 637 $ 654 $ 610
Estimated Future Benefit Payments	The following table represents estimated future Estimated Future Benefit Payments Pension PBOP SERP 2022 $ 7,040 $ 3,151 $ 637 2023 8,046 3,448 636 2024 8,497 3,559 635 2025 8,702 3,862 1,090 2026 9,804 4,158 1,144 2027—2031 54,565 23,853 5,583
Pension Plans
Schedule of Allocation of Plan Assets	The actual investment allocations are shown in the following tables. Pension Plan Target Actual Allocation at 2021 2020 2019 Equity Funds 56 % 57 % 58 % 54 % Debt Funds 39 % 38 % 37 % 36 % Real Estate Fund 5 % 4 % 4 % 9 % Other (1) — 1 % 1 % 1 % Total 100 % 100 % 100 % (1) Represents investments being held in cash equivalents as of December 31, 2021, December 31, 2020 and December 31, 2019 pending payment of benefits. Fair Value Measurements at Reporting Date Using Description Balance as of Quoted Significant Significant 2021 Pension Plan Assets: Mutual Funds: Equity Funds $ 86,356 $ 86,356 $ — $ — Fixed Income Funds 57,883 57,883 — — Total Mutual Funds 144,239 144,239 — — Cash Equivalents 912 912 Total Assets in the Fair Value Hierarchy $ 145,151 $ 145,151 $ — $ — Real Estate Fund–Measured at Net Asset Value 6,855 Total Assets $ 152,006 2020 Pension Plan Assets: Mutual Funds: Equity Funds $ 79,690 $ 79,690 $ — $ — Fixed Income Funds 50,622 50,622 — — Total Mutual Funds 130,312 130,312 — — Cash Equivalents 1,277 1,277 Total Assets in the Fair Value Hierarchy $ 131,589 $ 131,589 $ — $ — Real Estate Fund–Measured at Net Asset Value 5,817 Total Assets $ 137,406
Other Postretirement Benefit Plans, Defined Benefit
Schedule of Allocation of Plan Assets	The actual investment allocations are shown in the following tables. PBOP Plan Target Actual Allocation at 2021 2020 2019 Equity Funds 55 % 56 % 55 % 56 % Debt Funds 45 % 44 % 45 % 44 % Total 100 % 100 % 100 % Assets measured at fair value on a recurring basis for the PBOP Plan as of December 31, 2021 and 2020 are as follows (000’s): Fair Value Measurements at Reporting Date Using Description Balance as of Quoted Significant Significant 2021 PBOP Plan Assets: Mutual Funds: Fixed Income Funds $ 18,882 $ 18,882 $ — $ — Equity Funds 23,769 23,769 — — Total Assets $ 42,651 $ 42,651 $ — $ — 2020 PBOP Plan Assets: Mutual Funds: Fixed Income Funds $ 14,716 $ 14,716 $ — $ — Equity Funds 18,131 18,131 — — Total Assets $ 32,847 $ 32,847 $ — $ —

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) $ / shares in Units, $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2022$ / shares	Dec. 31, 2021USD ($)Subsidiarymi$ / shares	Dec. 31, 2020USD ($)$ / shares	Dec. 31, 2019USD ($)$ / shares	Dec. 31, 2018USD ($)
Significant Accounting Policies [Line Items]
Length Of Pipeline | mi		86
Gain on divestiture of business, pretax				$ 13.4
Gain on divestiture of business, net				9.8
Provision for income taxes				3.6
Cost of removal obligation		$ 107.5	$ 105.2
Regulatory assets		156.3	164.7
Investments in trading securities		$ 5.7	5.7
Number of Subsidiaries | Subsidiary		3
Allowance for doubtful accounts		$ 3.3	$ 3.3	$ 1	$ 1.3
Depreciation rate based on average depreciable property balance		3.29%	3.34%	3.41%
Common stock dividend per share, declared | $ / shares		$ 1.52	$ 1.50	$ 1.48
Increase in dividend declared amount per share | $ / shares		$ 1.52
Inventory of materials and supplies		$ 1	$ 0.6
Average Interest Rate On Debt		1.71%	3.12%	3.90%
Other Deferred Charges [Member]
Significant Accounting Policies [Line Items]
Regulatory assets		$ 15.3	$ 14.2
Materials And Supplies [Member]
Significant Accounting Policies [Line Items]
Inventory of materials and supplies		8.6	8.5
Subsequent Event [Member]
Significant Accounting Policies [Line Items]
Increase in dividend declared amount per share | $ / shares	$ 1.56
Unbilled Revenues
Significant Accounting Policies [Line Items]
Allowance for doubtful accounts		0.2	0.2
Accounts Receivable
Significant Accounting Policies [Line Items]
Allowance for doubtful accounts		$ 3.1	3.1
Utilities
Significant Accounting Policies [Line Items]
Number of Subsidiaries | Subsidiary		3
Unitil Service; Unitil Realty; and Unitil Resources
Significant Accounting Policies [Line Items]
Number of Subsidiaries | Subsidiary		3
Fitchburg Gas and Electric Light Company | Electric and Gas Division [Member] | Other Deferred Charges [Member]
Significant Accounting Policies [Line Items]
Hardship accounts in regulatory assets		$ 7.9	$ 6.8
Quarterly Payment [Member]
Significant Accounting Policies [Line Items]
Common stock dividend paid per share | $ / shares			$ 0.375	$ 0.37
Common stock dividend per share, declared | $ / shares		$ 0.38
Quarterly Payment [Member] | Subsequent Event [Member]
Significant Accounting Policies [Line Items]
Common stock dividend paid per share | $ / shares	0.39
Increase in dividend declared amount per share | $ / shares	$ 0.01
Annual Electric Sales Volume
Significant Accounting Policies [Line Items]
Percentage of total sales volumes revenue subject to RDM		27.00%
Annual Natural Gas Sales Volume
Significant Accounting Policies [Line Items]
Percentage of total sales volumes revenue subject to RDM		11.00%
Environmental and Rate Case Costs and Other Expenditures | Recovered over the next seven years
Significant Accounting Policies [Line Items]
Regulatory assets		$ 8.5
ISO-NE Obligations
Significant Accounting Policies [Line Items]
Cash Deposits		$ 2.7	$ 2.4
Maximum
Significant Accounting Policies [Line Items]
Lease term		12 months
Deferred Compensation Plan [Member]
Significant Accounting Policies [Line Items]
Investments in trading securities		$ 0.6	$ 0.5

Components of Gas and Electric

Components of Gas and Electric Operating Revenue (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	$ 473.3	$ 418.6	$ 437.3
Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	466.1	411.9	435.2
Rate Adjustment Mechanism Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	7.2	6.7	2.1
Gas Segment
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	224.8	191.4	203.4
Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	217.6	185.2	212.1
Gas Segment | Rate Adjustment Mechanism Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	7.2	6.2	(8.7)
Electric
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	248.5	227.2	233.9
Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	248.5	226.7	223.1
Electric | Rate Adjustment Mechanism Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	0	0.5	10.8
Residential | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	219	201.8	202.9
Residential | Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	83.9	73.1	81.4
Residential | Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	135.1	128.7	121.5
C&I | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	227.4	195.9	213.9
C&I | Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	124.1	104.5	120.1
C&I | Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	103.3	91.4	93.8
Other | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	19.7	14.2	18.4
Other | Gas Segment | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	9.6	7.6	10.6
Other | Electric | Billed and Unbilled Revenue
Operating Revenues [Line Items]
Total Gas and Electric Operating Revenues	$ 10.1	$ 6.6	$ 7.8

Components of Accrued Revenue (

Components of Accrued Revenue (Detail) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current	[1]	$ 47.4	$ 37.3
Total Accrued Revenue		61.2	50.9
Unbilled Revenues
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current		13.8	13.6
Regulatory Assets
Deferred Revenue Arrangement [Line Items]
Regulatory Assets – Current		$ 47.4	$ 37.3
[1]	Reflects amounts included in the Accrued Revenue on the Company’s Consolidated Balance Sheets.

Components of Exchange Gas Rece

Components of Exchange Gas Receivable (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Receivables [Line Items]
Total Exchange Gas Receivable	$ 7.4	$ 4.9
Northern Utilities Inc
Receivables [Line Items]
Total Exchange Gas Receivable	6.7	4.4
Fitchburg
Receivables [Line Items]
Total Exchange Gas Receivable	$ 0.7	$ 0.5

Components of Gas Inventory (De

Components of Gas Inventory (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 1	$ 0.6
Liquefied Natural Gas & Other
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	0.1	0.1
Natural Gas
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	0.5	0.2
Propane
Public Utilities, Inventory [Line Items]
Weighted average cost inventory amount	$ 0.4	$ 0.3

Regulatory Assets (Detail)

Regulatory Assets (Detail) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Regulatory Assets [Line Items]
Regulatory Assets		$ 156.3	$ 164.7
Less: Current Portion of Regulatory Assets	[1]	47.4	37.3
Regulatory Assets—noncurrent		108.9	127.4
Environmental Matters
Regulatory Assets [Line Items]
Regulatory Assets		4.6	5.2
Other Deferred Charges
Regulatory Assets [Line Items]
Regulatory Assets		15.3	14.2
Retirement Benefits
Regulatory Assets [Line Items]
Regulatory Assets		86.4	103.7
Deferred Storm Charges
Regulatory Assets [Line Items]
Regulatory Assets		3.3	4.1
Income Taxes
Regulatory Assets [Line Items]
Regulatory Assets		2.6	3.4
Energy Supply & Other Rate Adjustment Mechanisms
Regulatory Assets [Line Items]
Regulatory Assets		$ 44.1	$ 34.1
[1]	Reflects amounts included in the Accrued Revenue on the Company’s Consolidated Balance Sheets.

Regulatory Liabilities (Detail)

Regulatory Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2017
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 52.1	$ 49.8
Less: Current Portion of Regulatory Liabilities	9.5	5.5
Regulatory Liabilities-noncurrent	42.6	44.3
Rate Adjustment Mechanisms
Regulatory Liabilities [Line Items]
Regulatory Liabilities	7.7	4.1
Income Taxes
Regulatory Liabilities [Line Items]
Regulatory Liabilities	44.3	45.5	$ 48.9
Other
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$ 0.1	$ 0.2

Fair Value of Marketable Securi

Fair Value of Marketable Securities (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	$ 5.7	$ 5.7
Deferred Compensation Plan [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	0.6	0.5
Fair Value, Inputs, Level 1
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	5.7	5.7
Fair Value, Inputs, Level 1 | Deferred Compensation Plan [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	0.6	0.5
Fair Value, Inputs, Level 1 | Equity Funds | Deferred Compensation Plan [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	0.2	0.2
Fair Value, Inputs, Level 1 | Money Market Funds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	5.7	5.7
Fair Value, Inputs, Level 1 | Money Market Funds | Deferred Compensation Plan [Member]
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Trading Securities	$ 0.4	$ 0.3

Components of Energy Supply Obl

Components of Energy Supply Obligations (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Contractual Obligation [Line Items]
Energy Supply Obligations-Current	$ 14.5	$ 10.4
Renewable Energy Portfolio Standards
Contractual Obligation [Line Items]
Energy Supply Obligations-Current	7.8	5.7
Power Supply Contract Divestitures
Contractual Obligation [Line Items]
Energy Supply Obligations-Current	0	0.3
Exchange Gas Obligation
Contractual Obligation [Line Items]
Energy Supply Obligations-Current	$ 6.7	$ 4.4

Significant Segment Financial D

Significant Segment Financial Data (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other Operating Revenue – Non-Regulated			$ 0.9
Total Operating Revenues	$ 473.3	$ 418.6	438.2
Interest Income	1.6	2.6	2.9
Interest Expense	27.2	26.4	26.6
Depreciation & Amortization Expense	59.5	54.5	52
Income Tax Expense (Benefit)	11.5	10.2	13.8
Segment Profit (Loss)	36.1	32.2	44.2
Segment Assets	1,540.3	1,477.9	1,370.8
Capital Expenditures	115	122.6	119.2
Billed and Unbilled Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Operating Revenues	466.1	411.9	435.2
Rate Adjustment Mechanism Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Operating Revenues	7.2	6.7	2.1
Electric
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Operating Revenues	248.5	227.2	233.9
Interest Income	0.8	1.1	0.9
Interest Expense	9	8.7	9.4
Depreciation & Amortization Expense	25.9	23.8	22.6
Income Tax Expense (Benefit)	4.5	4.7	4.2
Segment Profit (Loss)	14	12.9	11.5
Segment Assets	584	571.8	529.3
Capital Expenditures	38.1	45.5	39.6
Electric | Billed and Unbilled Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Operating Revenues	248.5	226.7	223.1
Electric | Rate Adjustment Mechanism Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Operating Revenues	0	0.5	10.8
Gas Segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Operating Revenues	224.8	191.4	203.4
Interest Income	0.5	1.1	1.2
Interest Expense	15.3	14.2	14.4
Depreciation & Amortization Expense	32.6	29.8	28.5
Income Tax Expense (Benefit)	7.7	7.3	7.2
Segment Profit (Loss)	23.2	19.3	19.1
Segment Assets	935.9	886.3	823.3
Capital Expenditures	75.8	71.1	74
Gas Segment | Billed and Unbilled Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Operating Revenues	217.6	185.2	212.1
Gas Segment | Rate Adjustment Mechanism Revenue
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total Operating Revenues	7.2	6.2
All Other Segments
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Interest Income	0.3	0.4	0.6
Interest Expense	2.9	3.5	2.8
Depreciation & Amortization Expense	1	0.9	0.9
Income Tax Expense (Benefit)	(0.6)	(1.8)	(1.4)
Segment Profit (Loss)	(1.2)		3.4
Segment Assets	20.4	19.8	17.9
Capital Expenditures	1.1	$ 6	5.6
Unregulated Operation
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other Operating Revenue – Non-Regulated			0.9
Total Operating Revenues			0.9
Interest Income			0.2
Income Tax Expense (Benefit)	(0.1)		3.8
Segment Profit (Loss)	$ 0.1		10.2
Segment Assets			$ 0.3

Allowance for Doubtful Accoun_3

Allowance for Doubtful Accounts - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Recoveries	$ 0.8	$ 0.6	$ 0.8
Provision for Bad Debt	5.6	5.5	4.9
Allowance for doubtful accounts	3.3	3.3	1	$ 1.3
Unbilled Revenues
Financing Receivable, Impaired [Line Items]
Allowance for doubtful accounts	0.2	0.2
Accounts Receivable
Financing Receivable, Impaired [Line Items]
Allowance for doubtful accounts	3.1	3.1
Regulatory Assets Harship Accounts
Financing Receivable, Impaired [Line Items]
Recoveries	7.9	6.8
Energy Commodity
Financing Receivable, Impaired [Line Items]
Provision for Bad Debt	$ 2.4	$ 1.6	$ 2.3

Activity in Company's Allowance

Activity in Company's Allowance for Doubtful Accounts (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at Beginning of Period		$ 3.3	$ 1	$ 1.3
Provision		5.6	5.5	4.9
Recoveries		0.8	0.6	0.8
Accounts Written Off		6.5	4.4	6
Regulatory Defferals	[1]	0.1	0.6
Balance at End of Period		3.3	3.3	1
Electric
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at Beginning of Period		1.6	0.6	0.5
Provision		3.3	2.9	3
Recoveries		0.4	0.3	0.3
Accounts Written Off		3.4	2.6	3.2
Regulatory Defferals	[1]	0.1	0.4
Balance at End of Period		2	1.6	0.6
Gas
Accounts, Notes, Loans and Financing Receivable [Line Items]
Balance at Beginning of Period		1.7	0.4	0.8
Provision		2.3	2.6	1.9
Recoveries		0.4	0.3	0.5
Accounts Written Off		3.1	1.8	2.8
Regulatory Defferals	[1]		0.2
Balance at End of Period		$ 1.3	$ 1.7	$ 0.4
[1]	The Company has incurred greater than normal bad debt expense due to the coronavirus pandemic. Incremental bad debt expense amounts have been deferred as regulatory assets based on certain regulatory proceedings and management’s belief that such amounts are probable of recovery (See the “Financial Effects of COVID-19 Pandemic” section in Note 7 (Commitments and Contingencies). The Company will track the collection of receivables and to the extent incremental bad debt amounts are collected in the future, such amounts will reduce the regulatory assets recorded.

Debt and Financing Arrangemen_3

Debt and Financing Arrangements - Additional Information (Detail) - USD ($)	Dec. 18, 2020	Jul. 25, 2018	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Sep. 15, 2020	Dec. 18, 2019	Sep. 12, 2019	Oct. 30, 2015
Line of Credit Facility [Line Items]
Issuance of long-term debt	$ 100,000					$ 500,000	$ 200,000	$ 200,000
Weighted average interest rate on short term borrowings			1.20%	1.70%	3.40%
Guarantee outstanding			$ 700,000
Capital lease obligation, current			100,000
Accounts Payable			52,400,000	$ 33,200,000
Total rental expense under operating leases			1,900,000	1,800,000	$ 1,400,000
Operating lease obligations			1,900,000	1,800,000
Net Utility Plant			1,257,200,000	$ 1,193,200,000
Other current operating lease obligation			$ 1,600,000
Operating lease, weighted average remaining lease term			3 years 6 months	3 years 9 months 18 days
Operating lease, weighted average discount rate percentage			3.90%	4.40%
Restriction on retained earnings for dividend payments			Therefore, there were no restrictions on the Company’s Retained Earnings at December 31, 2021 for the payment of dividends.
Amount available for the payment of dividends			$ 166,900,000
Retained Earnings			116,200,000	$ 103,700,000
Long term debt repayments			$ 25,800,000	$ 24,800,000	18,800,000
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]			Other current operating lease obligation
Lease Obligations [Member]
Line of Credit Facility [Line Items]
Capital lease obligation, noncurrent			$ 200,000
Other noncurrent operating lease obligation			3,100,000
Unitil Energy, Fitchburg, Northern Utilities and Granite State
Line of Credit Facility [Line Items]
Amount available for the payment of dividends			$ 358,700,000
Credit Facility [Member] | Second Amended 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
Revolving credit facility termination date		Jul. 25, 2023
Increase in borrowing limit		$ 50,000,000
Credit Facility [Member] | London Interbank Offered Rate | Second Amended Credit Facility
Line of Credit Facility [Line Items]
Credit facility, daily fluctuating rate of interest		1.125%
3.43% Senior Notes, Due December 18, 2029
Line of Credit Facility [Line Items]
Long-term debt, stated interest rate			3.43%	3.43%
Long-term debt, maturity date			Dec. 18, 2029	Dec. 18, 2029
Bonds [Member]
Line of Credit Facility [Line Items]
Long term debt repayments			$ 25,800,000	$ 24,800,000	$ 18,800,000
Debt repayment, 2022			8,400,000
Debt repayment, 2023			6,900,000
Debt repayment, 2024			6,900,000
Debt repayment, 2025			5,000,000
Debt repayment, 2026			38,000,000
Debt repayment, Thereafter			444,400,000
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Revolving credit facility			120,000,000	120,000,000
Proceeds from lines of credit			239,100,000	248,900,000
Repayments of lines of credit			$ 229,700,000	252,800,000
Revolving Credit Facility [Member] | Credit Facility [Member]
Line of Credit Facility [Line Items]
Percentage of capitalization			The affirmative and negative covenants under the Credit Facility shall apply to Unitil 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 Unitil’s Funded Debt to Capitalization (as each term is defined in the Credit Facility) cannot exceed 65%, tested on a quarterly basis.
Accounts Payable				1,000,000
Natural gas storage inventory			$ 8,300,000	$ 5,400,000
Unitil Service Corp
Line of Credit Facility [Line Items]
Capital lease obligation, total capitalized cost									$ 13,400,000
Northern Utilities Inc
Line of Credit Facility [Line Items]
Accounts Payable			$ 1,600,000
Long-term debt, aggregate principal amount						40,000,000
Long-term debt, stated interest rate								4.04%
Total funded indebtedness as percentage of capitalization			65.00%
Northern Utilities Inc | 4.04% Senior Notes, Due September 12, 2049
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount								$ 40,000,000
Long-term debt, stated interest rate			4.04%	4.04%
Long-term debt, maturity date			Sep. 12, 2049	Sep. 12, 2049
Granite State Gas Transmission Inc
Line of Credit Facility [Line Items]
Total funded indebtedness as percentage of capitalization			65.00%
Fitchburg Gas and Electric Light Company
Line of Credit Facility [Line Items]
Total funded indebtedness as percentage of capitalization			65.00%
Fitchburg Gas and Electric Light Company | 3.78% Senior Notes, Due September 15, 2040
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount						$ 27,500,000
Long-term debt, stated interest rate						3.78%
Unitil Corporation | Maximum [Member]
Line of Credit Facility [Line Items]
Total funded indebtedness as percentage of capitalization			70.00%
Unitil Corporation | 3.43% Senior Notes, Due December 18, 2029
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount							$ 30,000,000
Long-term debt, stated interest rate							3.43%
Northern Utilities And Fitchburg | 3.78% Senior Notes, Due September 15, 2040
Line of Credit Facility [Line Items]
Long-term debt, stated interest rate						3.78%
Unitil Energy Systems Inc | 3.58% Mortgage Bonds, Due September 12, 2040
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount						$ 27,500,000
Long-term debt, stated interest rate						3.58%
Unitil Reality Corp | 2.64% Senior Secured Notes, Due December 18, 2030
Line of Credit Facility [Line Items]
Long-term debt, aggregate principal amount	$ 4,700,000
Long-term debt, stated interest rate	2.64%
Long-term debt, maturity date	Dec. 18, 2030
Assets under Capital Leases [Member]
Line of Credit Facility [Line Items]
Net Utility Plant			$ 700,000	$ 1,000,000
Net Utility Plant, accumulated amortization			$ 300,000	$ 500,000

Estimated Fair Value of Long Te

Estimated Fair Value of Long Term Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Fair Value, Inputs, Level 2
Debt Instrument [Line Items]
Estimated Fair Value of Long-Term Debt	$ 584.9	$ 633.1

Details on Long Term Debt (Deta

Details on Long Term Debt (Detail) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total Long-Term Debt		$ 509.6	$ 535.4
Less: Unamortized Debt Issuance Costs		3.6	3.8
Long-Term Debt		506	531.6
Less: Current Portion	[1]	8.2	8.5
Total Long-Term Debt, Less Current Portion		497.8	523.1
6.33% Senior Notes, Due May 1, 2022
Debt Instrument [Line Items]
Total Long-Term Debt			15
3.70% Senior Notes, Due August 1, 2026
Debt Instrument [Line Items]
Total Long-Term Debt		30	30
3.43% Senior Notes, Due December 18, 2029
Debt Instrument [Line Items]
Total Long-Term Debt		30	30
2.64% Senior Notes, Due December 18, 2030
Debt Instrument [Line Items]
Total Long-Term Debt		4.5	4.7
Unitil Energy Systems Inc | First Mortgage Bonds 8.49% Senior Secured Notes, Due October 14, 2024
Debt Instrument [Line Items]
Total Long-Term Debt		1.5	3
Unitil Energy Systems Inc | First Mortgage Bonds 6.96% Senior Secured Notes, Due September 1, 2028
Debt Instrument [Line Items]
Total Long-Term Debt		14	16
Unitil Energy Systems Inc | First Mortgage Bonds 8.00% Senior Secured Notes, Due May 1, 2031
Debt Instrument [Line Items]
Total Long-Term Debt		15	15
Unitil Energy Systems Inc | First Mortgage Bonds 6.32% Senior Secured Notes, Due September 15, 2036
Debt Instrument [Line Items]
Total Long-Term Debt		15	15
Unitil Energy Systems Inc | First Mortgage Bonds 3.58% Senior Secured Notes Due September 15, 2040
Debt Instrument [Line Items]
Total Long-Term Debt		27.5	27.5
Unitil Energy Systems Inc | First Mortgage Bonds 4.18% Senior Secured Notes Due November 30, 2048
Debt Instrument [Line Items]
Total Long-Term Debt		30	30
Fitchburg Gas and Electric Light Company | 6.75% Senior Notes, Due November 30, 2023
Debt Instrument [Line Items]
Total Long-Term Debt			1.9
Fitchburg Gas and Electric Light Company | 6.79% Senior Notes, Due October 15, 2025
Debt Instrument [Line Items]
Total Long-Term Debt		6	10
Fitchburg Gas and Electric Light Company | 3.52% Senior Notes, Due November 1, 2027
Debt Instrument [Line Items]
Total Long-Term Debt		10	10
Fitchburg Gas and Electric Light Company | 7.37% Senior Notes, Due January 15, 2029
Debt Instrument [Line Items]
Total Long-Term Debt		9.6	10.8
Fitchburg Gas and Electric Light Company | 5.90% Notes, Due December 15, 2030
Debt Instrument [Line Items]
Total Long-Term Debt		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
Fitchburg Gas and Electric Light Company | 3.78% Senior Notes, Due September 15, 2040
Debt Instrument [Line Items]
Total Long-Term Debt		27.5	27.5
Fitchburg Gas and Electric Light Company | 4.32% Senior Notes, Due November 1, 2047
Debt Instrument [Line Items]
Total Long-Term Debt		15	15
Northern Utilities Inc | 3.52% Senior Notes, Due November 1, 2027
Debt Instrument [Line Items]
Total Long-Term Debt		20	20
Northern Utilities Inc | 3.78% Senior Notes, Due September 15, 2040
Debt Instrument [Line Items]
Total Long-Term Debt		40	40
Northern Utilities Inc | 4.32% Senior Notes, Due November 1, 2047
Debt Instrument [Line Items]
Total Long-Term Debt		30	30
Northern Utilities Inc | 7.72% Senior Notes, Due December 3, 2038
Debt Instrument [Line Items]
Total Long-Term Debt		50	50
Northern Utilities Inc | 4.42% Senior Notes, Due October 15, 2044
Debt Instrument [Line Items]
Total Long-Term Debt		50	50
Northern Utilities Inc | 4.04% Senior Notes, Due September 12, 2049
Debt Instrument [Line Items]
Total Long-Term Debt		40	40
Granite State Gas Transmission Inc | 3.72% Senior Notes, Due November 1, 2027
Debt Instrument [Line Items]
Total Long-Term Debt		$ 15	$ 15
[1]	The Current Portion of Long-Term Debt includes sinking fund payments.

Details on Long Term Debt (Pare

Details on Long Term Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Sep. 12, 2019
Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate			4.04%
6.33% Senior Notes, Due May 1, 2022
Debt Instrument [Line Items]
Stated interest rate	6.33%	6.33%
Debt instrument due date	May 1, 2022	May 1, 2022
3.70% Senior Notes, Due August 1, 2026
Debt Instrument [Line Items]
Stated interest rate	3.70%	3.70%
Debt instrument due date	Aug. 1, 2026	Aug. 1, 2026
3.43% Senior Notes, Due December 18, 2029
Debt Instrument [Line Items]
Stated interest rate	3.43%	3.43%
Debt instrument due date	Dec. 18, 2029	Dec. 18, 2029
First Mortgage Bonds 8.49% Senior Secured Notes, Due October 14, 2024 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate	8.49%	8.49%
Debt instrument due date	Oct. 14, 2024	Oct. 14, 2024
First Mortgage Bonds 6.96% Senior Secured Notes, Due September 1, 2028 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate	6.96%	6.96%
Debt instrument due date	Sep. 1, 2028	Sep. 1, 2028
First Mortgage Bonds 8.00% Senior Secured Notes, Due May 1, 2031 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate	8.00%	8.00%
Debt instrument due date	May 1, 2031	May 1, 2031
First Mortgage Bonds 6.32% Senior Secured Notes, Due September 15, 2036 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate	6.32%	6.32%
Debt instrument due date	Sep. 15, 2036	Sep. 15, 2036
First Mortgage Bonds 3.58% Senior Secured Notes Due September 15, 2040 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate	3.58%	3.58%
Debt instrument due date	Sep. 15, 2040	Sep. 15, 2040
First Mortgage Bonds 4.18% Senior Secured Notes Due November 30, 2048 | Unitil Energy Systems Inc
Debt Instrument [Line Items]
Stated interest rate	4.18%	4.18%
Debt instrument due date	Nov. 30, 2048	Nov. 30, 2048
6.75% Senior Notes, Due November 30, 2023 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate	6.75%	6.75%
Debt instrument due date	Nov. 30, 2023	Nov. 30, 2023
6.79% Senior Notes, Due October 15, 2025 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate	6.79%	6.79%
Debt instrument due date	Oct. 15, 2025	Oct. 15, 2025
3.52% Senior Notes, Due November 1, 2027 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate	3.52%	3.52%
Debt instrument due date	Nov. 1, 2027	Nov. 1, 2027
3.52% Senior Notes, Due November 1, 2027 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate	3.52%	3.52%
Debt instrument due date	Nov. 1, 2027	Nov. 1, 2027
7.37% Senior Notes, Due January 15, 2029 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate	7.37%	7.37%
Debt instrument due date	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%
Debt instrument due date	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%
Debt instrument due date	Jun. 1, 2031	Jun. 1, 2031
3.78% Senior Notes, Due September 15, 2040 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate	3.78%	3.78%
Debt instrument due date	Sep. 15, 2040	Sep. 15, 2040
3.78% Senior Notes, Due September 15, 2040 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate	3.78%	3.78%
Debt instrument due date	Sep. 15, 2040	Sep. 15, 2040
4.32% Senior Notes, Due November 1, 2047 | Fitchburg Gas and Electric Light Company
Debt Instrument [Line Items]
Stated interest rate	4.32%	4.32%
Debt instrument due date	Nov. 1, 2047	Nov. 1, 2047
4.32% Senior Notes, Due November 1, 2047 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate	4.32%	4.32%
Debt instrument due date	Nov. 1, 2047	Nov. 1, 2047
7.72% Senior Notes, Due December 3, 2038 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate	7.72%	7.72%
Debt instrument due date	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%
Debt instrument due date	Oct. 15, 2044	Oct. 15, 2044
4.04% Senior Notes, Due September 12, 2049 | Northern Utilities Inc
Debt Instrument [Line Items]
Stated interest rate	4.04%	4.04%
Debt instrument due date	Sep. 12, 2049	Sep. 12, 2049
3.72% Senior Notes, Due November 1, 2027 | Granite State Gas Transmission Inc
Debt Instrument [Line Items]
Stated interest rate	3.72%	3.72%
Debt instrument due date	Nov. 1, 2027	Nov. 1, 2027
2.64% Senior Notes, Due December 18, 2030
Debt Instrument [Line Items]
Stated interest rate	2.64%	2.64%
Debt instrument due date	Dec. 18, 2030	Dec. 18, 2030

Summary of Interest Expense and

Summary of Interest Expense and Interest Income (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Interest Expense
Long-Term Debt		$ 26	$ 24.8	$ 22.9
Short-Term Debt		0.8	1.4	3
Regulatory Liabilities		0.4	0.2	0.7
Subtotal Interest Expense		27.2	26.4	26.6
Interest Income
Interest and Other Income		(1.6)	(2.6)	(2.9)
Total Interest Expense, Net		25.6	23.8	23.7
Regulatory Assets
Interest Income
Interest and Other Income		(0.5)	(0.8)	(0.8)
AFUDC and Other
Interest Income
Interest and Other Income	[1]	$ (1.1)	$ (1.8)	$ (2.1)
[1]	AFUDC—Allowance for Funds Used During Construction

Borrowing Limits Amounts Outsta

Borrowing Limits Amounts Outstanding and Amounts Available under Revolving Credit Facility (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Short-Term Borrowings Outstanding	$ 64.1	$ 54.7
Revolving Credit Facility
Debt Instrument [Line Items]
Revolving credit facility, limit	120	120
Short-Term Borrowings Outstanding	64.1	54.7
Letters of Credit Outstanding		0.1
Available revolving credit facility	$ 55.9	$ 65.2

Summary of Contractual Obligati

Summary of Contractual Obligations for Long-term Debt (Detail) $ in Millions	Dec. 31, 2021USD ($)
Contractual Obligation Fiscal Year Maturity Schedule [Line Items]
Total	$ 538.1
2022	59.7
2023	51.8
2024	40
2025	38.6
2026	38.2
2027 & Beyond	309.8
Long Term Debt Comprising Principal And Interest [Member]
Contractual Obligation Fiscal Year Maturity Schedule [Line Items]
Total	870.1
2022	32.9
2023	30.8
2024	30.3
2025	27.9
2026	60.6
2027 & Beyond	687.6
Long-Term Debt [Member] | Long Term Debt Comprising Principal And Interest [Member]
Contractual Obligation Fiscal Year Maturity Schedule [Line Items]
Total	509.6
2022	8.4
2023	6.9
2024	6.9
2025	5
2026	38
2027 & Beyond	444.4
Interest on Long-Term Debt [Member] | Long Term Debt Comprising Principal And Interest [Member]
Contractual Obligation Fiscal Year Maturity Schedule [Line Items]
Total	360.5
2022	24.5
2023	23.9
2024	23.4
2025	22.9
2026	22.6
2027 & Beyond	$ 243.2

Debt and Financing Arrangemen_4

Debt and Financing Arrangements - Classification of the Company Lease Obligations (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Operating Lease Obligations:
Other Current Liabilities (current portion)	$ 1,600
Capital Lease Obligations:
Other Current Liabilities (current portion)	100
Lease Obligations [Member]
Operating Lease Obligations:
Other Current Liabilities (current portion)	1,600	$ 1,500
Other Noncurrent Liabilities (long-term portion)	3,100	3,700
Total Operating Lease Obligations	4,670	5,200
Capital Lease Obligations:
Other Current Liabilities (current portion)	100	200
Other Noncurrent Liabilities (long-term portion)	200	200
Total Capital Lease Obligations	316	400
Total Lease Obligations	$ 5,000	$ 5,600

Future Operating Lease Payment

Future Operating Lease Payment Obligations and Future Minimum Lease Payments under Capital Leases (Detail) - Lease Obligations [Member] - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Operating leases
2022	$ 1,695
2023	1,399
2024	1,069
2025	503
2026	199
2027-2031	121
Total Payments	4,986
Less: Interest	316
Amount of Lease Obligations Recorded on Consolidated Balance Sheets	4,670	$ 5,200
Capital lease
2022	150
2023	107
2024	52
2025	19
Total Payments	328
Less: Interest	12
Amount of Lease Obligations Recorded on Consolidated Balance Sheets	$ 316	$ 400

Equity - Additional Information

Equity - Additional Information (Detail) - USD ($)	Jan. 25, 2022	Aug. 06, 2021	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Class of Stock [Line Items]
Common stock, shares outstanding			15,977,766	15,012,310
Common stock, shares issued		800,000	942,316	23,658	20,065
Common stock, shares authorized			25,000,000	25,000,000
Common stock price per share		$ 50.80
Proceeds from Issuance of Common Stock			$ 45,500,000	$ 1,100,000	$ 1,100,000
Percentage of fully-vested restricted stock units that directors will receive in common shares when settled			70.00%
Common stock shares repurchase			8,012	13,194	2,911
Fair value of liabilities associated with fully vested RSUs that will be settled in cash			$ 1,000,000	$ 800,000
Share based compensation expense			$ 1,400,000	2,200,000	$ 2,300,000
Percentage of fully-vested restricted stock units that directors will receive in cash when settled			30.00%
Preferred Stock			$ 200,000	$ 200,000
Proceeds from Issuance Initial Public Offering		$ 38,600,000
Restricted Stock
Class of Stock [Line Items]
Restricted stock vesting period			4 years
Restricted stock non-vested			37,621	39,426
Restricted stock weighted average grant date fair value			$ 49.72	$ 55.46
Unrecognized share based compensation			$ 600,000
Share compensation recognition period			2 years 6 months
Cancellations under the stock plan			0
Restricted Stock | Subsequent Event
Class of Stock [Line Items]
Restricted Stock Units Granted	36,770
Aggregate Market Value	$ 1,700,000
Restricted Stock | Vesting Annually
Class of Stock [Line Items]
Restricted stock vesting percentage annually				25.00%
Unitil Energy Systems Inc | Series 6
Class of Stock [Line Items]
Preferred stock, outstanding			1,861	1,887
Preferred Stock			$ 200,000	$ 200,000
Dividend rate			6.00%	6.00%
Dividend and Distribution Reinvestment and Share Purchase Plan
Class of Stock [Line Items]
Proceeds from Issuance of Common Stock			$ 1,000,000	$ 1,100,000	$ 1,100,000
Dividend and Distribution Reinvestment and Share Purchase Plan | Common Stock
Class of Stock [Line Items]
Common stock, shares issued			22,316	23,658	20,065
Over-Allotment Option [Member]
Class of Stock [Line Items]
Number Of Shares Granted Overallotment Option To Purchase Additional Shares		30 days
Sale of Stock, Number of Shares Issued in Transaction		120,000
Proceeds from Issuance of Private Placement		$ 5,900,000
Maximum
Class of Stock [Line Items]
Dividend declared			$ 100,000	$ 100,000
Repurchase expense			$ 400,000	$ 500,000	$ 200,000
Maximum | Restricted Stock
Class of Stock [Line Items]
Restricted stock available for awards			677,500
Restricted stock that may be awarded in any one calendar year to any one participant			20,000
Average | Dividend and Distribution Reinvestment and Share Purchase Plan
Class of Stock [Line Items]
Common stock price per share			$ 46.98

Restricted Shares Issued in Con

Restricted Shares Issued in Conjunction with Stock Plan (Detail) - Restricted Stock $ in Millions	12 Months Ended
	Dec. 31, 2021USD ($)shares
Period 1
Class of Stock [Line Items]
Issuance Date	Jan. 29, 2019
Shares | shares	33,150
Aggregate Market Value | $	$ 1.6
Period 2
Class of Stock [Line Items]
Issuance Date	Jan. 28, 2020
Shares | shares	28,630
Aggregate Market Value | $	$ 1.8
Period 3
Class of Stock [Line Items]
Issuance Date	Jul. 28, 2020
Shares | shares	3,000
Aggregate Market Value | $	$ 0.1
Period 4
Class of Stock [Line Items]
Issuance Date	Jan. 26, 2021
Shares | shares	23,140
Aggregate Market Value | $	$ 0.9

Restricted Stock Units Issued (

Restricted Stock Units Issued (Detail) - Restricted Stock Units (RSUs) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Restricted Stock Units
Beginning Restricted Stock Units	43,192	70,364
Restricted Stock Units Granted	4,519	3,743
Dividend Equivalents Earned	1,471	1,507
Restricted Stock Units Settled		(32,422)
Ending Restricted Stock Units	49,182	43,192
Weighted-Average Stock Price
Beginning Restricted Stock Units	$ 41.34	$ 41.20
Restricted Stock Units Granted	43.35	39.26
Dividend Equivalents Earned	46.34	47.34
Restricted Stock Units Settled		41.09
Ending Restricted Stock Units	$ 41.67	$ 41.34

Reconciliation of Basic and Dil

Reconciliation of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Schedule Of Computation Of Basic And Diluted Earnings Per Common Share [Line Items]
Earnings Available to Common Shareholders	$ 36.1	$ 32.2	$ 44.2
Weighted Average Common Shares Outstanding—Basic	15,373	14,951	14,894
Plus: Diluted Effect of Incremental Shares	3	1	6
Weighted Average Common Shares Outstanding—Diluted	15,376	14,952	14,900
Earnings per Share—Basic and Diluted	$ 2.35	$ 2.15	$ 2.97

Weighted Average Non Vested Res

Weighted Average Non Vested Restricted Shares Excluded from Computation of Earnings Per Share (Detail) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Non Vested Restricted Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted Average Non-Vested Restricted Shares Not Included in EPS Computation	23,636	42,813

Energy Supply - Additional Info

Energy Supply - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2021BcfMMBTU
Northern Utilities Inc
Gas and Oil Acreage [Line Items]
Natural gas available under firm contract per day of year-round and seasonal transportation and underground storage capacity to distribution facilities | MMBTU	122,000,000,000
Natural gas, underground storage | Bcf	4,300,000,000
Northern Utilities Inc | Maximum
Gas and Oil Acreage [Line Items]
Purchases of natural gas, contract duration	1 year
Fitchburg Gas and Electric Light Company
Gas and Oil Acreage [Line Items]
Natural gas available under firm contract per day of year-round and seasonal transportation and underground storage capacity to distribution facilities | MMBTU	14,439
Natural gas, underground storage | Bcf	0.4
Percentage of power supply requirement	50.00%
Power supply contract duration	12 months
Unitil Energy Systems Inc
Gas and Oil Acreage [Line Items]
Percentage of power supply requirement	100.00%
Power supply contract duration	6 months

Gas And Electric Supply Contrac

Gas And Electric Supply Contractual Obligations (Detail) $ in Millions	Dec. 31, 2021USD ($)
Total	$ 538.1
2022	59.7
2023	51.8
2024	40
2025	38.6
2026	38.2
2027 & Beyond	309.8
Gas Supply Contracts
Total	523.9
2022	58.5
2023	50.6
2024	38.8
2025	37.3
2026	36.9
2027 & Beyond	301.8
Electric Supply Contracts
Total	14.2
2022	1.2
2023	1.2
2024	1.2
2025	1.3
2026	1.3
2027 & Beyond	$ 8

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)

Nov. 02, 2021USD ($)

Oct. 01, 2021USD ($)

Aug. 24, 2021USD ($)

Aug. 02, 2021USD ($)

May 27, 2021USD ($)

May 01, 2021USD ($)

Apr. 02, 2021USD ($)

Jan. 31, 2021USD ($)

Nov. 30, 2020USD ($)

Nov. 02, 2020USD ($)

Mar. 26, 2020USD ($)

Feb. 28, 2020USD ($)

Oct. 29, 2019USD ($)

Jun. 25, 2019

Nov. 01, 2018USD ($)

Mar. 31, 2021USD ($)

Dec. 31, 2021USD ($)Bcf

Dec. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Dec. 17, 2021Bcf

Oct. 29, 2021USD ($)

Oct. 30, 2020USD ($)

Jan. 10, 2020MWh

May 23, 2019MWh

Jul. 31, 2018MWMWh

Jun. 30, 2017MWMWh

Commitments And Contingencies [Line Items]

Corporate income tax rate

21.00%

21.00%

21.00%

Spending cap

$ 538,100,000

Power generation facility | Bcf

1,600

Approved annual increase in rates

$ 3,600,000

$ 4,600,000

$ 3,700,000

Increase in annual base rate

3.60%

Requested annual increase in rates

$ 1,100,000

Tax Year 2018

Commitments And Contingencies [Line Items]

Corporate income tax rate

21.00%

21.00%

Other Restructuring

Commitments And Contingencies [Line Items]

Cost recovery period, years

2 years

Vinyard Wind Energy [Member]

Commitments And Contingencies [Line Items]

Power generation facility | Bcf

1,200

Mayflower Wind energy [Member]

Commitments And Contingencies [Line Items]

Power generation facility | Bcf

400

Northern Utilities Inc

Commitments And Contingencies [Line Items]

Approved annual increase in rates

$ 4,500,000

$ 12,000,000

Increase in annual base rate

4.40%

Northern Utilities Inc | New Hampshire

Commitments And Contingencies [Line Items]

Approved annual increase in rates

$ 2,600,000

Requested annual increase in rates

$ 7,800,000

Percentage of change in revenue over previous year

8.10%

Northern Utilities Inc | Maine

Commitments And Contingencies [Line Items]

Percentage of approved return on equity, reflecting on equity

50.00%

Percentage of approved return on equity, reflecting on debt

50.00%

Percentage of approved return on equity

9.48%

Fitchburg Gas and Electric Light Company

Commitments And Contingencies [Line Items]

Increase (decrease) in annual revenue

$ 1,600,000

$ 1,400,000

Power generation capacity | MWh

9,450,000

Percentage of approved return on equity, reflecting on equity

52.45%

Percentage of approved return on equity, reflecting on debt

47.55%

Percentage of approved return on equity

9.70%

Revenue Impact Threshold

$ 100,000

Requested annual increase in rates

$ 1,100,000

$ 900,000

Fitchburg Gas and Electric Light Company | Offshore Wind Energy

Commitments And Contingencies [Line Items]

Power generation facility | MW

400

1,600

Remuneration Percentage

2.75%

Fitchburg Gas and Electric Light Company | Offshore Wind Energy | First Solicitation [Member]

Commitments And Contingencies [Line Items]

Power generation facility

800

800

Fitchburg Gas and Electric Light Company | Offshore Wind Energy | Second Solicitation [Member]

Commitments And Contingencies [Line Items]

Power generation facility | MWh

800

Fitchburg Gas and Electric Light Company | Offshore Wind Energy | Third Solicitation [Member]

Commitments And Contingencies [Line Items]

Power generation facility | Bcf

1,600

Facility power capacity to be procured in the future | Bcf

2,400

Fitchburg Gas and Electric Light Company | Offshore Wind Energy | Maximum [Member] | Third Solicitation [Member]

Commitments And Contingencies [Line Items]

Power generation facility | Bcf

5,600

Fitchburg Gas and Electric Light Company | Qualified Clean Energy

Commitments And Contingencies [Line Items]

Power generation capacity | MWh

9,554,940

Remuneration Percentage

2.75%

Fitchburg Gas Company

Commitments And Contingencies [Line Items]

Percentage of approved return on equity, reflecting on equity

52.45%

Percentage of approved return on equity, reflecting on debt

47.55%

Percentage of approved return on equity

9.70%

Revenue Impact Threshold

$ 40,000

Regulatory assets approved increase in revenue due to be recovered

$ 3,300,000

$ 2,200,000

Approved annual increase in rates

$ 900,000

$ 1,100,000

Approved annual increase in rates

$ 900,000

Apporved annual decrease in rates

200,000

Granite State

Commitments And Contingencies [Line Items]

Increase (decrease) in annual revenue

$ 100,000

$ 1,300,000

Spending cap

$ 14,600,000

Company's Liability for Environ

Company's Liability for Environmental Obligations (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Environmental Exit Cost [Line Items]
Total Balance at Beginning of Period	$ 2.1	$ 2.7
Additions	0.9	0.2
Less: Payments / Reductions	0.3	0.8
Total Balance at End of Period	2.7	2.1
Less: Current Portion	0.5	0.3
Noncurrent Balance at End of Period	$ 2.2	$ 1.8

Provisions for Federal and Stat

Provisions for Federal and State Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Current Income Tax Provision
Federal		$ 0.3
State	$ 0.7	0.6	$ 0.3
Total Current Income Taxes	0.7	0.9	0.3
Deferred Income Tax Provision
Federal	7.3	6.5	9.4
State	3.5	2.8	4.1
Total Deferred Income Taxes	10.8	9.3	13.5
Total Income Tax Expense	$ 11.5	$ 10.2	$ 13.8

Differences Between Provisions

Differences Between Provisions for Income Taxes and Provisions Calculated at Statutory Federal Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Examination [Line Items]
Statutory Federal Income Tax Rate	21.00%	21.00%	21.00%
State Income Taxes, net	6.00%	6.00%	6.00%
Utility Plant Differences	(3.00%)	(4.00%)	(3.00%)
Other, net		1.00%
Effective Income Tax Rate	24.00%	24.00%	24.00%

Deferred Tax Assets and Liabili

Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred Tax Assets
Retirement Benefit Obligations	$ 34.1	$ 40.7
Net Operating Loss Carryforwards	4.1
Tax Credit Carryforwards	0.7	0.3
Other, net	1.3	1.3
Total Deferred Tax Assets	40.2	42.3
Deferred Tax Liabilities
Utility Plant Differences	157.4	143.8
Regulatory Assets & Liabilities	9.4	6.2
Other, net	1.1	1.3
Total Deferred Tax Liabilities	167.9	151.3
Net Deferred Tax Liabilities	$ 127.7	$ 109

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes [Line Items]
Corporate federal income tax		21.00%	21.00%	21.00%
Regulatory Liability	$ 49.8	$ 52.1	$ 49.8
Regulatory liability, expected flow back to customers		47.1				$ 48.9
Regulatory liability, expected pass back to ratepayers		$ 0.7	0.3	$ 1.7		1.8
Net Operating Loss Carryforwards Utilized For Income Taxes			7.7
Percentage of employment retention credit		50.00%
Employment retention duties capacity		100.00%
Employment tax expense		$ 0.4	0.6
Consolidated Appropriations Act 2021 [Member]
Income Taxes [Line Items]
Percentage of employment retention credit	70.00%
Employment retention duties capacity	100.00%
Minimum
Income Taxes [Line Items]
Average Rate Assumption Method estimated flow back period		15 years
Maximum
Income Taxes [Line Items]
Average Rate Assumption Method estimated flow back period		20 years
Income Tax Related Liabilities
Income Taxes [Line Items]
Regulatory Liability	$ 45.5	$ 44.3	$ 45.5			$ 48.9
Gas Ratepayers | Massachusetts And Maine [Member]
Income Taxes [Line Items]
Regulatory liability, expected flow back to customers		3.1
Net Operating Loss Carryforward Assets
Income Taxes [Line Items]
Regulatory liability, expected pass back to ratepayers		$ 3.6			$ 2
Tax Year 2018
Income Taxes [Line Items]
Corporate federal income tax					21.00%	21.00%

Key Weighted Average Assumption

Key Weighted Average Assumptions Used in Determining Benefit Plan Costs and Obligations (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Benefit Plan Costs
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.50%	3.25%	4.25%
Rate of Compensation Increase	3.00%	3.00%	3.00%
Expected Long-term rate of return on plan assets	7.50%	7.40%	7.50%
Health Care Cost Trend Rate Assumed for Next Year	6.60%	7.00%	7.00%
Ultimate Health Care Cost Trend Rate	4.50%	4.50%	4.50%
Year that Ultimate Health Care Cost Trend Rate is reached	2029	2029	2024
Benefit Obligation
Defined Benefit Plan Disclosure [Line Items]
Discount Rate	2.85%	2.50%	3.25%
Rate of Compensation Increase	3.00%	3.00%	3.00%
Health Care Cost Trend Rate Assumed for Next Year	6.20%	6.60%	7.00%
Ultimate Health Care Cost Trend Rate	4.50%	4.50%	4.50%
Year that Ultimate Health Care Cost Trend Rate is reached	2029	2029	2029

Retirement Benefit Obligations

Retirement Benefit Obligations - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Change in Discount Rate	0.25%
Increase or decrease of Net Periodic Benefit Cost (NPBC) due to change in the discount rate	$ 679
Pension expense	7,200	$ 6,900	$ 5,800
Regulatory assets	$ 156,300	164,700
Defined Benefit Plan, Expected Long-term Rate-of-Return on Assets Assumption	The desired investment objective is a long-term rate of return on assets that is approximately 5 – 6% greater than the assumed rate of inflation as measured by the Consumer Price Index.
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation	$ 185,100	189,400
Company's contributions	4,100	4,665	6,916
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Company's contributions	8,903	4,156	4,000
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Accumulated Benefit Obligation	17,500	16,700
Company's contributions	637	654	610
Fair Value Of Plan Assets
Defined Benefit Plan Disclosure [Line Items]
Pension expense	6,100	6,500	7,300
Defined Benefit Obligations
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	86,400	103,700
Four Zero One K Plan
Defined Benefit Plan Disclosure [Line Items]
Company's contributions	$ 3,300	$ 3,000	$ 2,800
Benefit Plan Costs
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Long-term Return on Assets	7.50%	7.40%	7.50%
Scenario Forecast | Pension Plans | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations				56.00%
Scenario Forecast | Pension Plans | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations				39.00%
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations				55.00%
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations				45.00%
Real Estate Funds | Scenario Forecast | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations				5.00%

Components of Retirement Plan C

Components of Retirement Plan Costs (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 3,472	$ 3,322	$ 3,104
Interest Cost	5,003	5,776	6,484
Expected Return on Plan Assets	(9,693)	(9,019)	(8,475)
Prior Service Cost Amortization	301	320	320
Actuarial Loss Amortization	8,089	6,472	4,324
Sub-total	7,172	6,871	5,757
Amounts Capitalized or Deferred	(3,384)	(3,083)	(2,227)
NPBC Recognized	3,788	3,788	3,530
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service Cost	3,034	2,698	2,304
Interest Cost	2,740	3,121	3,426
Expected Return on Plan Assets	(2,508)	(2,063)	(1,645)
Prior Service Cost Amortization	1,208	1,210	1,213
Actuarial Loss Amortization	1,045	744	227
Sub-total	5,519	5,710	5,525
Amounts Capitalized or Deferred	(3,136)	(2,865)	(2,317)
NPBC Recognized	2,383	2,845	3,208
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Service Cost	354	283	247
Interest Cost	458	549	567
Prior Service Cost Amortization	56	57	56
Actuarial Loss Amortization	1,489	1,036	628
Sub-total	2,357	1,925	1,498
Amounts Capitalized or Deferred	(712)	(579)	(430)
NPBC Recognized	$ 1,645	$ 1,346	$ 1,068

Summary of Information on Plans

Summary of Information on Plans' Assets, Projected Benefit Obligations (PBO), and Funded Status (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Beginning of Year	$ 137,406	$ 125,755
Actual Return on Plan Assets	16,989	13,024
Employer Contributions	4,100	4,665	$ 6,916
Benefits Paid	(6,489)	(6,038)
Plan Assets at End of Year	152,006	137,406	125,755
PBO at Beginning of Year	206,092	182,135
Service Cost	3,472	3,322	3,104
Interest Cost	5,003	5,776	6,484
Plan Amendments	674	732
Benefits Paid	(6,489)	(6,038)	(6,877)
Actuarial (Gain) or Loss	(9,334)	20,165
PBO at End of Year	199,418	206,092	182,135
Funded Status: Assets vs PBO	(47,412)	(68,686)
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Plan Assets at Beginning of Year	32,847	27,280
Actual Return on Plan Assets	3,586	3,739
Employer Contributions	8,903	4,156	4,000
Participant Contributions	220	240
Benefits Paid	(2,905)	(2,568)
Plan Assets at End of Year	42,651	32,847	27,280
PBO at Beginning of Year	106,831	95,657
Service Cost	3,034	2,698	2,304
Interest Cost	2,740	3,121	3,426
Benefits Paid	(2,905)	(2,568)	(1,758)
Actuarial (Gain) or Loss	2,167	7,683
PBO at End of Year	112,087	106,831	95,657
Funded Status: Assets vs PBO	(69,436)	(73,984)
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Employer Contributions	637	654	610
Benefits Paid	(637)	(654)
PBO at Beginning of Year	20,225	17,759
Service Cost	354	283	247
Interest Cost	458	549	567
Benefits Paid	(637)	(654)	(610)
Actuarial (Gain) or Loss	(2,686)	2,288
PBO at End of Year	17,714	20,225	$ 17,759
Funded Status: Assets vs PBO	$ (17,714)	$ (20,225)

Employer Contributions, Partici

Employer Contributions, Participant Contributions and Benefit Payments (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plans
Defined Contribution Plan Disclosure [Line Items]
Employer Contributions	$ 4,100	$ 4,665	$ 6,916
Benefit Payments	6,489	6,038	6,877
Other Postretirement Benefit Plans, Defined Benefit
Defined Contribution Plan Disclosure [Line Items]
Employer Contributions	8,903	4,156	4,000
Participant Contributions	220	240	121
Benefit Payments	2,905	2,568	1,758
Supplemental Employee Retirement Plans, Defined Benefit
Defined Contribution Plan Disclosure [Line Items]
Employer Contributions	637	654	610
Benefit Payments	$ 637	$ 654	$ 610

Estimated Future Benefit Paymen

Estimated Future Benefit Payments (Detail) $ in Thousands	Dec. 31, 2021USD ($)
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
2022	$ 7,040
2023	8,046
2024	8,497
2025	8,702
2026	9,804
2027 — 2031	54,565
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
2022	3,151
2023	3,448
2024	3,559
2025	3,862
2026	4,158
2027 — 2031	23,853
Supplemental Employee Retirement Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
2022	637
2023	636
2024	635
2025	1,090
2026	1,144
2027 — 2031	$ 5,583

Actual Investment Allocations (

Actual Investment Allocations (Detail)		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation			100.00%	100.00%	100.00%
Pension Plans | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation			57.00%	58.00%	54.00%
Pension Plans | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation			38.00%	37.00%	36.00%
Pension Plans | Other
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	[1]		1.00%	1.00%	1.00%
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation			100.00%	100.00%	100.00%
Other Postretirement Benefit Plans, Defined Benefit | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation			56.00%	55.00%	56.00%
Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation			44.00%	45.00%	44.00%
Real Estate Funds | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation			4.00%	4.00%	9.00%
Scenario Forecast | Pension Plans | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		56.00%
Scenario Forecast | Pension Plans | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		39.00%
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		55.00%
Scenario Forecast | Other Postretirement Benefit Plans, Defined Benefit | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		45.00%
Scenario Forecast | Real Estate Funds | Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		5.00%
[1]	Represents investments being held in cash equivalents as of December 31, 2021, December 31, 2020 and December 31, 2019 pending payment of benefits.

Assets Measured at Fair Value o

Assets Measured at Fair Value on Recurring Basis for Pension Plan (Detail) - Pension Plans - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	$ 152,006	$ 137,406	$ 125,755
Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	144,239	130,312
Mutual Fund | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	86,356	79,690
Mutual Fund | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	57,883	50,622
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	912	1,277
Mutual Fund Including Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	145,151	131,589
Real Estate Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	6,855	5,817
Fair Value, Inputs, Level 1 | Mutual Fund
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	144,239	130,312
Fair Value, Inputs, Level 1 | Mutual Fund | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	86,356	79,690
Fair Value, Inputs, Level 1 | Mutual Fund | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	57,883	50,622
Fair Value, Inputs, Level 1 | Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	912	1,277
Fair Value, Inputs, Level 1 | Mutual Fund Including Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	$ 145,151	$ 131,589

Assets Measured at Fair Value_2

Assets Measured at Fair Value on Recurring Basis for PBOP Plan (Detail) - Other Postretirement Benefit Plans, Defined Benefit - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	$ 42,651	$ 32,847	$ 27,280
Mutual Fund | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	18,882	14,716
Mutual Fund | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	23,769	18,131
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	42,651	32,847
Fair Value, Inputs, Level 1 | Mutual Fund | Fixed Income Securities
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	18,882	14,716
Fair Value, Inputs, Level 1 | Mutual Fund | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Plan assets measured at fair value	$ 23,769	$ 18,131