Summary of Significant Accounting Policies (Details) (USD $)	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011
Revenue
Maturity period of commercial paper	90 days
Period within which revenues and associated costs reported as net regulatory balancing accounts related to the WRAM and MCBA that are deferred, are Not expected to be collected	24 months
Expected collection period for operating income reported as net regulatory balancing accounts related to the WRAM and MCBA that are deferred	24 months
Unearned revenue liability	$ 1,500,000		$ 1,700,000
Operating Revenues
Net WRAM and MCBA deferral at the beginning of the period	882,000	12,864,000
Less: reversal of prior year deferral during the period	(1,911,000)	(12,295,000)
Add: net WRAM and MCBA deferral during the period	2,764,000	939,000
Net amount during the period	853,000	(11,356,000)
Net WRAM and MCBA deferral at the end of the period	1,735,000	1,508,000
Operating Costs
Net WRAM and MCBA deferral at the beginning of the period	719,000	10,492,000
Less: reversal of prior year deferral during the period	(1,603,000)	(10,027,000)
Add: net WRAM and MCBA deferral during the period	2,375,000	766,000
Net amount during the period	772,000	(9,261,000)
Net WRAM and MCBA deferral at the end of the period	1,491,000	1,231,000
Income Before Income Taxes
Net WRAM and MCBA deferral at the beginning of the period	163,000	2,372,000
Less: reversal of prior year deferral during the period	(308,000)	(2,268,000)
Add: net WRAM and MCBA deferral during the period	389,000	173,000
Net amount during the period	81,000	(2,095,000)
Net WRAM and MCBA deferral at the end of the period	244,000	277,000
Markup for return or profit for cost-recovery expenses	0
Regulatory Assets and Liabilities
Net short-term regulatory balancing accounts (receivable)	27,047,000		34,020,000
Net long-term regulatory assets (receivable)	354,879,000		344,419,000
Net short-term regulatory balancing accounts (liability)	1,699,000		5,018,000
Cash and Cash Equivalents
Cash and cash equivalents	48,847,000	16,971,000	38,790,000	27,203,000
Restricted cash	1,100,000		2,300,000
Minimum
Regulatory Assets and Liabilities
Expected collection period for undercollected net WRAM and MCBA receivables	12 months
Maximum
Regulatory Assets and Liabilities
Expected collection period for undercollected net WRAM and MCBA receivables	18 months
Net WRAM and MCBA accounts payable
Regulatory Assets and Liabilities
Net short-term regulatory balancing accounts (liability)	174,000		371,000
Net long-term regulatory liability	108,000		119,000
Total regulatory liabilities	282,000		490,000
Net WRAM and MCBA accounts receivable
Regulatory Assets and Liabilities
Net short-term regulatory balancing accounts (receivable)	27,047,000		34,020,000
Net long-term regulatory assets (receivable)	21,925,000		12,051,000
Total regulatory assets	$ 48,972,000		$ 46,071,000