Dividend Limitations (Details)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Dividend limitations
Common shareholder’s equity	$ 529,945,000	$ 494,297,000	$ 465,945,000	$ 506,801,000
Retained Earnings (Accumulated Deficit)	279,821,000	247,065,000
AWR
Dividend limitations
Common shareholder’s equity	529,945,000	494,297,000
Subsidiaries [Member]
Dividend limitations
Dividends paid	36,500,000	33,800,000	62,000,000
GSWC
Dividend limitations
Fixed amount in computing maximum ability to pay dividends	$ 21,000,000.0
Percentage of consolidated net income plus the aggregate net cash proceeds received from capital stock offerings or other instruments convertible into capital stock	100.00%
Amount available to pay dividends under the most restrictive of the Note Agreements	$ 400,800,000
Dividends paid	27,680,000	25,450,000	62,000,000
Common shareholder’s equity	$ 474,374,000	446,770,000	423,730,000	435,190,000
Ratio of Indebtedness to Net Capital	0.4332
Retained Earnings (Accumulated Deficit)		206,288,000
GSWC | Maximum
Dividend limitations
Ratio of Indebtedness to Net Capital	0.6667
Earnings Reinvested in the Business
Dividend limitations
Common shareholder’s equity	$ 279,821,000	247,065,000	220,923,000	253,602,000
Earnings Reinvested in the Business | GSWC
Dividend limitations
Common shareholder’s equity	232,193,000	$ 206,288,000	$ 184,935,000	$ 199,583,000
Retained Earnings (Accumulated Deficit)	232,193,000
Earnings Reinvested in the Business | American States Utility Services [Member]
Dividend limitations
Retained Earnings (Accumulated Deficit)	$ 62,000,000