Regulatory Matters (Details 10) (GSWC, USD $)	1 Months Ended	12 Months Ended
	Nov. 30, 2011 item	Dec. 31, 2012	Sep. 30, 2012	Oct. 02, 2012	Jan. 02, 2012
Regulatory matters:
Weighted cost of capital (return on rate base), with an updated embedded debt cost and the settlement ROE (as a percent)		8.64%
Cost of Capital Proceeding for Water Regions
Regulatory matters:
Settlement agreement, number of other California water utilities	3
Authorized ROE under settlement agreement (as a percent)					9.99%
Settlement agreement, percentage of equity in rate-making capital structure					55.00%
Settlement agreement, percentage of debt in rate-making capital structure					45.00%
Weighted cost of capital (return on rate base), with an updated embedded debt cost and the settlement ROE (as a percent)					8.64%
Refunds provided to customers		$ 408,000
Period of cost of capital proceedings for adjustment in ROE and rate of return		3 years
Difference adjustment in ROE (as a percent)		50.00%
Decrease in Moody's rate from benchmark (as a percent)			1.12%
Decrease in ROE (as a percent)		0.56%
Proposed authorized ROE under the settlement agreement (as a percent)				9.43%
Cost of Capital Proceeding for Water Regions | Minimum
Regulatory matters:
Change in average of the Moody's Aa utility bond rate (as a percent)		1.00%