Regulatory Matters (Details 3) (GSWC, USD $)	12 Months Ended
	Dec. 31, 2012 MWh	Dec. 31, 2011
Regulatory matters:
Under (over) collection	$ 176,015,000	$ 179,957,000
Electric supply cost balancing account
Regulatory matters:
Under (over) collection	5,558,000	8,347,000
Decrease in under-collection	2,800,000
Megawatts of electric energy provided under purchased power contract	13
Fixed price of electric energy per MWh	67.90
Surcharge per kilowatt-hour authorized by CPUC for collection	2.2
Electric supply cost balancing account | Settled suit
Regulatory matters:
Under (over) collection	5,100,000
Monthly payments required under settlement	38,000
Purchased energy and power system delivery costs
Regulatory matters:
Under (over) collection	$ 458,000
Authorized weighted average annual cost of power purchased per megawatt-hour for including amounts in balancing account	77