Bank Debt (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Bank debt
Maximum borrowing capacity	$ 150,000,000.0
Short-term borrowing activities (excluding letters of credit)
Balance outstanding at the end of the period	0	$ 59,000,000
Long-term borrowing [Member]
Short-term borrowing activities (excluding letters of credit)
Balance outstanding at the end of the period	$ 95,500,000
Short-term borrowing (excluding letters of credit)
Short-term borrowing activities (excluding letters of credit)
Balance outstanding at the end of the period		$ 59,000,000
Interest Rate at the end of the period (as a percent)	3.19%	2.28%
Average amount outstanding	$ 69,559,000	$ 65,242,000
Weighted Average Annual Interest Rate (as a percent)	2.66%	1.69%
Maximum Amount Outstanding	$ 95,500,000	$ 102,500,000
Syndicated revolving credit facility
Bank debt
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
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]
Bank debt
Letter of credit, amount	$ 15,000,000
AWR
Bank debt
Maximum borrowing capacity	150,000,000
Short-term borrowing activities (excluding letters of credit)
Balance outstanding at the end of the period	$ 0	$ 59,000,000
AWR | Syndicated revolving credit facility
Short-term borrowing activities (excluding letters of credit)
Interest coverage ratio	623.00%
Total funded debt ratio	43.00%
AWR | Syndicated revolving credit facility | Minimum
Short-term borrowing activities (excluding letters of credit)
Interest coverage ratio	325.00%
Total funded debt ratio	65.00%
AWR | Syndicated revolving credit facility | Maximum
Short-term borrowing activities (excluding letters of credit)
Total funded debt ratio	100.00%
AWR | Syndicated revolving credit facility | Letters of credit
Bank debt
Maximum borrowing capacity	$ 25,000,000
Letter of credit, amount	$ 900,000
Letter of credit fee (as a percent)	0.65%
AWR | Syndicated revolving credit facility | Letter of Credit Business Automobile Insurance Policy Security [Member]
Bank debt
Letter of credit, amount	$ 340,000
AWR | Syndicated revolving credit facility | Letter of Credit - Purchase of power
Bank debt
Letter of credit, amount	$ 585,000,000