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Summary of Significant Accounting Policies: (Details)		3 Months Ended		6 Months Ended
Summary of Significant Accounting Policies: (Details)	Jul. 01, 2020 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) customer registrant	Jun. 30, 2019 USD ($)	Jul. 15, 2020 USD ($)	Jul. 08, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Summary of significant accounting policies
Increase to provision		$ 673,000		$ 1,066,000
Earnings reinvested in the business		363,065,000		363,065,000					$ 345,964,000
Operating lease right-of-use assets		$ 11,967,000		$ 11,967,000					13,168,000
Nature of Operations:
Number of customers \| customer				1,000,000
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		$ 200,000,000		$ 200,000,000					200,000,000
Notes payable to banks		49,000,000		$ 49,000,000					5,000,000
Related Party Transaction, Terms and Manner of Settlement				P24M
Syndicated Credit Facility
Related Party Transactions
Maximum borrowing capacity on line of credit		249,000,000.0		$ 249,000,000.0
AWR \| Syndicated Credit Facility
Related Party Transactions
Line of Credit Facility, Incremental Expansion of Borrowing Capacity								$ 35,000,000.0
GOLDEN STATE WATER COMPANY
Summary of significant accounting policies
Increase to provision		673,000		1,066,000
Earnings reinvested in the business		266,973,000		266,973,000					257,434,000
Operating lease right-of-use assets		11,720,000		11,720,000					12,745,000
Related Party Transactions
Payments to affiliate for corporate office administrative and general costs		1,200,000	$ 1,300,000	2,700,000	$ 2,400,000
Intercompany payable to Parent		$ 199,235,000		$ 199,235,000					$ 158,845,000
GOLDEN STATE WATER COMPANY \| Water Service Utility Operations
Nature of Operations:
Number of customers \| customer				261,000
GOLDEN STATE WATER COMPANY \| Electric Service Utility Operations
Nature of Operations:
Number of customers \| customer				24,000
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 \| AWR \| Syndicated Credit Facility
Related Party Transactions
Line of Credit Facility, Current Borrowing Capacity								200,000,000.0
Maximum \| AWR \| Syndicated Credit Facility
Related Party Transactions
Line of Credit Facility, Current Borrowing Capacity								$ 260,000,000.0
Subsequent Event [Member] \| GOLDEN STATE WATER COMPANY \| Private Placement Notes
Related Party Transactions
Debt Instrument, Face Amount							$ 160,000,000.0
Subsequent Event [Member] \| GOLDEN STATE WATER COMPANY \| Note Payable 2.17 Percent Due 2030
Related Party Transactions
Debt Instrument, Face Amount							$ 85,000,000.0
Debt Instrument, Interest Rate, Stated Percentage							2.17%
Subsequent Event [Member] \| GOLDEN STATE WATER COMPANY \| Note Payables 2.9% Percent Due 2040
Related Party Transactions
Debt Instrument, Face Amount							$ 75,000,000.0
Debt Instrument, Interest Rate, Stated Percentage							2.90%
Subsequent Event [Member] \| Bear Valley Electric Service
Related Party Transactions
Debt Instrument, Term	3 years
Subsequent Event [Member] \| Bear Valley Electric Service \| Syndicated Credit Facility
Related Party Transactions
Line of Credit Facility, Current Borrowing Capacity	$ 35,000,000
Line of Credit Facility, Incremental Expansion of Borrowing Capacity	$ 15,000,000
Subsequent Event [Member] \| Minimum \| AWR \| Syndicated Credit Facility
Related Party Transactions
Line of Credit Facility, Current Borrowing Capacity						$ 200,000,000.0