Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 registrant	Dec. 31, 2011	Dec. 31, 2010
Basis of Presentation:
Number of registrants filing combined report	2
Goodwill
Goodwill arose from acquisition of subcontractor's business	$ 1,100,000	$ 1,100,000
Interest
Amount of capital projects authorized by the CPUC to be filed for revenue recovery with advice letters			18,500,000
Sales and Use Taxes:
Non-income tax assessments accounted on a gross basis	15,381,000	14,210,000	14,165,000
GSWC
Property and Depreciation
Net credit acquisition adjustment included in utility plant	8,800,000
Amortization period of acquisition adjustment permitted by CPUC	30 years
Amortization of the acquisition adjustments	374,000	374,000	374,000
Depreciation on transportation equipment	1,800,000	2,500,000	2,200,000
Estimated useful lives of utility plant, as authorized by the CPUC
Generation	P40Y
Interest
Amount recorded in AFUDC	299,000
Weighted cost of capital (as a percent)	8.64%
Alternative-Revenue Programs
Number of months within which expected additional revenue collection is recorded	24 months
Advances for Construction and Contributions in aid of Constructions
Period for refund of advances for construction	40 years
Fair Value of Financial Instruments
Long-term debt-GSWC	456,792,000
Sales and Use Taxes:
Franchise fees billed to customers and recorded as operating revenue	3,400,000	3,200,000	3,300,000
Non-income tax assessments accounted on a gross basis	13,835,000	12,851,000	12,658,000
GSWC | Level 2
Fair Value of Financial Instruments
Long-term debt-GSWC	456,792,000
GSWC | Carrying Amount
Fair Value of Financial Instruments
Long-term debt-GSWC	335,791,000	340,686,000
GSWC | Fair Value
Fair Value of Financial Instruments
Long-term debt-GSWC	456,792,000	437,275,000
GSWC | Minimum
Estimated useful lives of utility plant, as authorized by the CPUC
Source of water supply	30 years
Pumping	25 years
Water treatment	20 years
Transmission and distribution	P25Y
Other plant	P7Y
Interest
Expected completion period of advice letter projects	2 years
GSWC | Maximum
Estimated useful lives of utility plant, as authorized by the CPUC
Source of water supply	50 years
Pumping	40 years
Water treatment	35 years
Transmission and distribution	P55Y
Other plant	P40Y
Interest
Expected completion period of advice letter projects	3 years
GSWC | Purchase, production, distribution and sale of water
Nature of Operations:
Number of customers served	256,000
Property and Depreciation
Aggregate composite rate for depreciation (as a percent)	3.70%	3.80%	3.80%
GSWC | Electricity distribution
Nature of Operations:
Number of customers served	23,000
Property and Depreciation
Aggregate composite rate for depreciation (as a percent)	3.60%	3.70%	3.70%
ASUS
Sales and Use Taxes:
Non-income tax assessments accounted on a gross basis	717,000	718,000	890,000
ASUS | Contracts
Nature of Operations:
Period of fixed price contracts to operate and maintain the water and/or wastewater systems at various military bases	50 years
AWR | Syndicated Credit Facility
Related Party Transactions
Maximum borrowing capacity on line of credit	$ 100,000,000