Dividend Limitations (Details)	12 Months Ended
	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Dividend limitations
Common shareholder’s equity ( Note 20)	$ 641,673,000	$ 601,530,000	$ 558,223,000	$ 529,945,000
Reinvested earnings in the business	385,007,000	345,964,000
AWR
Dividend limitations
Common shareholder’s equity ( Note 20)	641,673,000	601,530,000
Subsidiaries [Member]
Dividend limitations
Dividends paid	47,300,000	42,700,000	79,000,000.0
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	$ 576,400,000
Dividends paid	22,500,000	20,200,000	68,850,000
Common shareholder’s equity ( Note 20)	$ 583,298,000	551,188,000	503,575,000	474,374,000
Ratio of Indebtedness to Net Capital	0.4306
Reinvested earnings in the business	$ 228,392,000	257,434,000
GSWC | Maximum
Dividend limitations
Ratio of Indebtedness to Net Capital	0.6667
Earnings Reinvested in the Business
Dividend limitations
Common shareholder’s equity ( Note 20)	$ 385,007,000	345,964,000	304,534,000	279,821,000
Earnings Reinvested in the Business | GSWC
Dividend limitations
Common shareholder’s equity ( Note 20)	$ 228,392,000	$ 257,434,000	$ 211,163,000	$ 232,193,000