Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026 USD ($) state contract	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($) state customer contract registrant	Jun. 30, 2025 USD ($)
Summary of significant accounting policies
Number of customers | customer			1,000,000
Number of states in which entity operates | state	10		10
Number of registrants filing combined report | registrant			2
GSWC | Notes Payable 5.50 Percent Due 2027
Summary of significant accounting policies
Stated interest rate percentage	5.50%		5.50%
Face amount of debt | $	$ 65.0		$ 65.0
GSWC | Water:
Summary of significant accounting policies
Number of customers | customer			265,200
BVES
Summary of significant accounting policies
Payments to affiliate for corporate office administrative and general costs | $	0.8	$ 0.8	$ 1.9	$ 1.9
BVES | Electric:
Summary of significant accounting policies
Number of customers | customer			24,900
ASUS
Summary of significant accounting policies
Payments to affiliate for corporate office administrative and general costs | $	$ 1.2	$ 1.2	$ 2.9	$ 2.8
Bay State Utility Service LLC (" BSUS")
Summary of significant accounting policies
Number of contracts with 15 year contract | contract	1		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