Dividend Limitations (Details)	12 Months Ended
	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2016 USD ($)
Dividend limitations
Common shareholder’s equity	$ 601,530,000	$ 558,223,000	$ 529,945,000		$ 494,297,000
Reinvested earnings in the business	345,964,000	304,534,000		$ 0
AWR
Dividend limitations
Common shareholder’s equity	601,530,000	558,223,000
Subsidiaries [Member]
Dividend limitations
Dividends paid	42,700,000	79,000,000.0	36,500,000
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	$ 473,900,000
Dividends paid	20,200,000	68,850,000	27,680,000
Common shareholder’s equity	$ 551,188,000	503,575,000	474,374,000		446,770,000
Ratio of Indebtedness to Net Capital	0.4445
Reinvested earnings in the business	$ 257,434,000	211,163,000
GSWC | Maximum
Dividend limitations
Ratio of Indebtedness to Net Capital	0.6667
Earnings Reinvested in the Business
Dividend limitations
Common shareholder’s equity	$ 345,964,000	304,534,000	279,821,000		247,065,000
Earnings Reinvested in the Business | GSWC
Dividend limitations
Common shareholder’s equity	257,434,000	$ 211,163,000	$ 232,193,000		$ 206,288,000
Earnings Reinvested in the Business | American States Utility Services [Member]
Dividend limitations
Reinvested earnings in the business	$ 62,100,000