SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 M D	Dec. 31, 2011
Revenue
Maturity period of commercial paper (in days)	90
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 (in months)	12
Expected collection period for operating income reported as net regulatory balancing accounts related to the WRAM and MCBA that are deferred (in months)	24
Unearned revenue liability	$ 1,708	$ 1,871
Operating Revenues
Net WRAM and MCBA deferral at the beginning of the period	12,864
Reversal of deferred amounts during the period	(12,864)
Deferred amounts added during the period	882
Net WRAM and MCBA deferral at the end of the period	882
Operating Costs
Net WRAM and MCBA deferral at the beginning of the period	10,492
Reversal of deferred amounts during the period	(10,492)
Deferred amounts added during the period	719
Net WRAM and MCBA deferral at the end of the period	719
Income Before Income Taxes
Net WRAM and MCBA deferral at the beginning of the period	2,372
Reversal of deferred amounts during the period	(2,372)
Deferred amounts added during the period	163
Net WRAM and MCBA deferral at the end of the period	163
Regulatory Assets and Liabilities
Net short-term receivable	34,020	21,680
Net long-term receivable	344,419	319,898
Total receivable	344,419	319,898
Net short-term payable	5,018	2,655
Total payable	35,720	28,037
Minimum
Regulatory Assets and Liabilities
Expected collection period for undercollected net WRAM and MCBA receivables (in months)	12
Maximum
Regulatory Assets and Liabilities
Expected collection period for undercollected net WRAM and MCBA receivables (in months)	18
Net WRAM and MCBA accounts payable
Regulatory Assets and Liabilities
Net short-term payable	371	543
Net long-term payable	119	145
Total payable	490	688
Net WRAM and MCBA accounts receivable
Regulatory Assets and Liabilities
Net short-term receivable	34,020	19,357
Net long-term receivable	12,051	30,268
Total receivable	$ 42,071	$ 49,625