SCHEDULE I - CONDENSED FINANCIAL INFORMATION OF PARENT 4 (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2016	Sep. 30, 2016	Oct. 27, 2015
Short-term borrowing activities (excluding letters of credit)
Balance outstanding at the end of the period	$ 90,000,000	$ 28,000,000
Short-term borrowing (excluding letters of credit)
Short-term borrowing activities (excluding letters of credit)
Balance outstanding at the end of the period	$ 90,000,000	$ 28,000,000
Interest Rate at the end of the period (as a percent)	1.46%	1.09%
Average Amount Outstanding	$ 59,261,000	$ 4,112,000
Weighted Average Annual Interest Rate (as a percent)	1.20%	0.92%
Maximum Amount Outstanding	$ 96,000,000	$ 37,000,000
Syndicated revolving credit facility
Note payable to banks
Variable rate basis	Euro rate
Syndicated revolving credit facility | Minimum
Short-term borrowing activities (excluding letters of credit)
Interest coverage ratio	325.00%
Syndicated revolving credit facility | Maximum [Member]
Short-term borrowing activities (excluding letters of credit)
Total funded debt ratio	65.00%
Syndicated revolving credit facility | Letter of Credit Irrevocable Franchise Agreement with City of Rancho Cordova [Member]
Note payable to banks
Letter of credit, amount	$ 15,000,000
AWR
Note payable to banks
Maximum borrowing capacity				$ 150,000,000	$ 100,000,000.0
Short-term borrowing activities (excluding letters of credit)
Balance outstanding at the end of the period	$ 90,000,000	28,000,000
AWR | Syndicated revolving credit facility
Short-term borrowing activities (excluding letters of credit)
Interest coverage ratio	707.00%
Total funded debt ratio	46.00%
AWR | Syndicated revolving credit facility | Minimum
Short-term borrowing activities (excluding letters of credit)
Interest coverage ratio	325.00%
AWR | Syndicated revolving credit facility | Maximum [Member]
Short-term borrowing activities (excluding letters of credit)
Total funded debt ratio	65.00%
AWR | Syndicated revolving credit facility | Letters of credit
Note payable to banks
Maximum borrowing capacity	$ 25,000,000
Letter of credit, amount	$ 9,900,000
Letter of credit fee (as a percent)	0.65%
AWR | Syndicated revolving credit facility | Letter of Credit - GSWC business automobile insurance policy
Note payable to banks
Letter of credit, amount	$ 340,000
AWR | Syndicated revolving credit facility | Letter of Credit - American Recovery and Reinvestment Act
Note payable to banks
Letter of credit, amount	5,400,000
AWR | Syndicated revolving credit facility | Letter of Credit - Purchase of power
Note payable to banks
Letter of credit, amount	585,000,000
AWR | Syndicated revolving credit facility | Irrevocable Letter of Credit - Edison Settlement agreement
Note payable to banks
Letter of credit, amount	3,600,000
Subsidiaries [Member]
Short-term borrowing activities (excluding letters of credit)
Dividends paid	(33,800,000)		$ (52,000,000)
GSWC
Short-term borrowing activities (excluding letters of credit)
Dividends paid	(25,450,000)	(62,000,000)	$ (52,000,000)
Syndicated revolving credit facility | AWR | Syndicated revolving credit facility
Note payable to banks
Maximum borrowing capacity	150,000,000
Notes Payable, Other Payables [Member] | GSWC
Short-term borrowing activities (excluding letters of credit)
Debt Instrument, Face Amount						$ 40,000,000
Debt Instrument, Maximum Borrowing Capacity						40,000,000
Notes Payable, Other Payables [Member] | American States Utility Services [Member]
Short-term borrowing activities (excluding letters of credit)
Debt Instrument, Face Amount						10,000,000
Debt Instrument, Maximum Borrowing Capacity						$ 10,000,000
Notes Receivable | Notes Payable, Other Payables [Member] | AWR
Short-term borrowing activities (excluding letters of credit)
Notes Receivable, Related Parties, Current		$ 0			$ 0
Notes Receivable | Notes Payable, Other Payables [Member] | GSWC
Short-term borrowing activities (excluding letters of credit)
Notes Receivable, Related Parties, Current	$ 0