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Summary of Significant Accounting Policies: (Details) customer in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Nov. 30, 2020	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) registrant customer	Sep. 30, 2018 USD ($)	Oct. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Summary of significant accounting policies
Earnings reinvested in the business		$ 340,539,000		$ 340,539,000				$ 0	$ 304,534,000
Operating lease right-of-use assets		$ 13,017,000		$ 13,017,000				7,600,000	0
Nature of Operations:
Number of customers \| customer				1,000,000,000
Number of States in which Entity Operates		9		9
Basis of Presentation:
Number of registrants filing combined report \| registrant				2
Related Party Transactions
Notes payable to bank		$ 194,500,000		$ 194,500,000					95,500,000
Related Party Transaction, Terms and Manner of Settlement				P24M
Total lease obligations		13,377,000		$ 13,377,000				$ 8,000,000.0
AWR \| Syndicated Credit Facility
Related Party Transactions
Maximum borrowing capacity on line of credit							$ 200,000,000.0
GOLDEN STATE WATER COMPANY
Summary of significant accounting policies
Earnings reinvested in the business		245,496,000		245,496,000					211,163,000
Operating lease right-of-use assets		12,494,000		12,494,000					0
Related Party Transactions
Payments to affiliate for corporate office administrative and general costs		1,200,000	$ 1,200,000	3,500,000	$ 3,200,000
Intercompany payable to Parent		151,240,000		$ 151,240,000					$ 57,289,000
GOLDEN STATE WATER COMPANY \| Notes Payable 6.7 Percent Due 2019 [Member]
Related Party Transactions
Debt and Capital Lease Obligations							$ 40,000,000.0
Debt Instrument, Interest Rate, Stated Percentage							6.70%
GOLDEN STATE WATER COMPANY \| Water Service Utility Operations
Nature of Operations:
Number of customers \| customer				261
GOLDEN STATE WATER COMPANY \| Electric Service Utility Operations
Nature of Operations:
Number of customers \| customer				24
ASUS \| Contracted Services
Nature of Operations:
Period of fixed price contracts to operate and maintain water systems at various military bases				50 years
Sales \| GOLDEN STATE WATER COMPANY \| Water Service Utility Operations
Nature of Operations:
Concentration Risk, Percentage				90.00%
Sales \| GOLDEN STATE WATER COMPANY \| Electric Service Utility Operations
Nature of Operations:
Concentration Risk, Percentage				90.00%
Minimum [Member] \| AWR \| Syndicated Credit Facility
Related Party Transactions
Line of Credit Facility, Current Borrowing Capacity							$ 150,000,000.0
Subsequent Event [Member]
Related Party Transactions
Related Party Transaction, Terms and Manner of Settlement	P24M
Subsequent Event [Member] \| AWR \| Syndicated Credit Facility
Related Party Transactions
Maximum borrowing capacity on line of credit						$ 225,000,000.0
Line of Credit Facility, Incremental Expansion of Borrowing Capacity						$ 25,000,000.0
Long-term Debt [Member] \| GOLDEN STATE WATER COMPANY
Related Party Transactions
Intercompany payable to Parent		$ 151,200,000		$ 151,200,000