Summary of Significant Accounting Policies (Details) $ in Thousands				1 Months Ended	3 Months Ended					9 Months Ended
	Aug. 01, 2024 USD ($)	Jul. 01, 2024 USD ($)	Apr. 15, 2024 USD ($)	Sep. 30, 2024 USD ($) item state shares	Sep. 30, 2024 USD ($) item state shares	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($) shares	Mar. 31, 2023 USD ($)	Sep. 30, 2024 USD ($) customer registrant item state shares	Sep. 30, 2023 USD ($) shares	Jun. 05, 2024 USD ($)	Feb. 27, 2024 USD ($)	Dec. 31, 2023 USD ($)
Summary of significant accounting policies
Number of customers | customer										1,000,000
Number of states in which entity operates | state				10	10					10
Number of military bases started operating in April 2024 | item										2
Number of registrants filing combined report | registrant										2
Sale of stock, maximum consideration on transaction													$ 200,000
Agreement term (in years)										3 years
Sale of stock, number of shares issued in transaction (in shares) | shares					335,449					791,097
Sale of stock, consideration received on transaction					$ 27,000					$ 60,000
Payments for commissions					400					900
Payments of stock issuance costs					100					800
Sale of Stock, remaining available for sale				$ 139,100	139,100					$ 139,100
Debt instrument term (in years)										5 years
Notes payable to banks				120,000	120,000					$ 120,000				$ 291,500
Issuance of Common Shares from an at-the-market program, net of issuance costs					26,881	$ 16,724	$ 15,584
Notes payable to banks				177,000	177,000					177,000				42,000
Syndicated Revolving Credit Facility
Summary of significant accounting policies
Notes payable to banks				120,000	120,000					120,000
GSWC
Summary of significant accounting policies
Notes payable to banks				0	0					$ 0				150,000
Intercompany borrowings payment term										24 months
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares) | shares								1			1
Issuance of Common Shares from an at-the-market program, net of issuance costs								$ 10,000	$ 10,000		$ 10,000
Notes payable to banks				140,000	140,000					$ 140,000				$ 0
GSWC | Unsecured Private Placement Notes
Summary of significant accounting policies
Face amount of debt												$ 65,000
Stated interest rate percentage												5.50%
GSWC | Syndicated Revolving Credit Facility
Summary of significant accounting policies
Notes payable to banks				140,000	140,000					$ 140,000
GSWC | Water:
Summary of significant accounting policies
Number of customers | customer										264,600
BVES
Summary of significant accounting policies
Payments to affiliate for corporate office administrative and general costs					700			700		$ 2,400	2,800
Intercompany borrowings payment term										24 months
Maximum borrowing capacity on line of credit				$ 65,000	65,000					$ 65,000
Issuance of Common Shares from an at-the-market program, net of issuance costs (in shares) | shares				11
Issuance of Common Shares from an at-the-market program, net of issuance costs				$ 22,000
BVES | Financing Application
Summary of significant accounting policies
Requested deferment period	9 months
Regulatory rate case filings requested authorization for debt and equity issuance	$ 120,000
BVES | Syndicated Revolving Credit Facility
Summary of significant accounting policies
Notes payable to banks				$ 37,000	37,000					$ 37,000
BVES | Electric:
Summary of significant accounting policies
Number of customers | customer										24,800
ASUS
Summary of significant accounting policies
Payments to affiliate for corporate office administrative and general costs					$ 1,200			$ 1,100		$ 4,000	$ 3,800
Bay State Utility Service LLC (" BSUS")
Summary of significant accounting policies
Number of contracts with 15 year contract | item				1	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
Initial price contract value					$ 75,000
JBCC approved task order value for the first year			$ 4,100
Patuxent River Utility Services LLC ( PRUS) | Contracted services:
Summary of significant accounting policies
Period of fixed price contracts to operate and maintain water systems at various military bases										50 years
Initial price contract value										$ 349,000
Revised price contract value after an inventory adjustment		$ 378,000
Maximum | Syndicated Revolving Credit Facility
Summary of significant accounting policies
Current borrowing capacity				$ 165,000	165,000					165,000
Maximum | GSWC | Syndicated Revolving Credit Facility
Summary of significant accounting policies
Current borrowing capacity				$ 200,000	$ 200,000					$ 200,000
Maximum | ASUS
Summary of significant accounting policies
Period of fixed price contracts to operate and maintain water systems at various military bases										50 years