SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Revenue
Markup for return or profit for cost-recovery expenses	$ 0
Maturity period of commercial paper	90 days
Minimum collection period after net receivable balances were recognized in which the Company defers net WRAM and MCBA operating revenues and associated costs	12 months
Maximum collection period in which deferred net WRAM and MCBA revenues and associated costs will be recognized	24 months
Unearned revenue liability	$ 700,000	$ 800,000
Asset retirement obligation	$ 21,200,000	$ 20,300,000
Regulatory Assets and Liabilities
Expected collection period for undercollected net WRAM and MCBA receivables	18 months
Minimum
Regulatory Assets and Liabilities
Expected collection period for undercollected net WRAM and MCBA receivables	12 months