v3.26.1
Summary of Significant Accounting Policies (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2026
USD ($)
contract
customer
state
registrant
Mar. 31, 2025
USD ($)
Summary of significant accounting policies    
Number of customers 1,000,000  
Number of states in which entity operates | state 10  
Number of registrants filing combined report | registrant 2  
GSWC | Water:    
Summary of significant accounting policies    
Number of customers 265,100  
BVES    
Summary of significant accounting policies    
Payments to affiliate for corporate office administrative and general costs | $ $ 1.1 $ 1.0
BVES | Electric:    
Summary of significant accounting policies    
Number of customers 24,900  
ASUS    
Summary of significant accounting policies    
Payments to affiliate for corporate office administrative and general costs | $ $ 1.7 $ 1.6
Bay State Utility Service LLC (" BSUS")    
Summary of significant accounting policies    
Number of contracts with 15 year contract | contract 1  
Bay State Utility Service LLC (" BSUS") | Contracted services:    
Summary of significant accounting policies    
Period of fixed price contracts to operate and maintain water systems at various military bases 15 years  
Maximum | ASUS    
Summary of significant accounting policies    
Period of fixed price contracts to operate and maintain water systems at various military bases 50 years