XML 38 R26.htm IDEA: XBRL DOCUMENT v3.22.2
Summary of Significant Accounting Policies - Additional Information (Detail)
$ in Millions
 6 Months Ended
Jun. 30, 2022
USD ($)
Subsidiary
mi
Dec. 31, 2021
USD ($)
Jun. 30, 2021
USD ($)
Significant Accounting Policies [Line Items]      
Number of Subsidiaries | Entity | Subsidiary 3    
Length Of Pipeline | mi 86    
Cost of removal obligation $ 112.4 $ 107.5 $ 105.1
Investments in trading securities 5.4 5.7 5.5
Allowance for doubtful accounts 2.7 3.3 4.6
Regulatory assets 148.0 156.3 156.1
Other Deferred Charges [Member]      
Significant Accounting Policies [Line Items]      
Regulatory assets 13.3 15.3 17.8
Unbilled Revenues [member]      
Significant Accounting Policies [Line Items]      
Allowance for doubtful accounts 0.1 0.2 0.1
Accounts Receivable [member]      
Significant Accounting Policies [Line Items]      
Allowance for doubtful accounts $ 2.6 3.1 4.5
Utilities      
Significant Accounting Policies [Line Items]      
Number of Subsidiaries | Entity | Subsidiary 3    
Unitil Service; Unitil Realty; and Unitil Resources      
Significant Accounting Policies [Line Items]      
Number of Subsidiaries | Entity | Subsidiary 3    
Fitchburg Gas And Electric Light Company [Member] | Other Deferred Charges [Member] | Electric And Gas Division [Member]      
Significant Accounting Policies [Line Items]      
Hardship accounts in regulatory assets $ 7.6 7.9 9.8
Environmental and Rate Case Costs and Other Expenditures | Recovered over the next seven years      
Significant Accounting Policies [Line Items]      
Regulatory assets 6.6    
ISO-NE Obligations      
Significant Accounting Policies [Line Items]      
Cash Deposits $ 1.7 2.7 1.5
Maximum      
Significant Accounting Policies [Line Items]      
Lease term 12 months    
Deferred Compensation Plan [Member]      
Significant Accounting Policies [Line Items]      
Investments in trading securities $ 0.8 $ 0.6 $ 0.7