SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 6) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulatory Assets and Liabilities
Regulatory Assets	$ 355,930	$ 361,893
Regulatory Liabilities	38,735	35,264
Short-term portion of the regulatory assets	30,332	35,052
Short-term portion of the regulatory liabilities	4,759	2,227
Long-Term Debt Premium, Discount and Expense
Amortization of debt premium and expenses	871	825	$ 797
Advances for Construction
Advances for construction	$ 182,448	180,172
Refund period	40 years
Estimated refunds of advances
2017	$ 7,900
2018	7,700
2019	7,700
2020	7,600
2021	7,600
Future tax benefits due ratepayers
Regulatory Assets and Liabilities
Regulatory Liabilities	33,231	29,505
Conservation program
Regulatory Assets and Liabilities
Regulatory Liabilities	584	2,317
Net WRAM and MCBA long-term payable
Regulatory Assets and Liabilities
Regulatory Liabilities	611	488
Pension balancing account
Regulatory Assets and Liabilities
Regulatory Liabilities	695	792
Other Liabilities
Regulatory Assets and Liabilities
Regulatory Liabilities	3,614	2,162
Pension and retiree group health
Regulatory Assets and Liabilities
Regulatory Assets	188,880	205,614
Future tax benefits due ratepayers
Regulatory Assets and Liabilities
Regulatory Assets	92,099	81,522
Other accrued benefits
Regulatory Assets and Liabilities
Regulatory Assets	27,503	27,327
Interim rates long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory Assets	4,605	5,238
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory Assets	16,148	15,410
Asset retirement obligations, net
Regulatory Assets and Liabilities
Regulatory Assets	15,812	14,682
Tank Coating
Regulatory Assets and Liabilities
Regulatory Assets	8,452	6,829
Health care balancing account
Regulatory Assets and Liabilities
Regulatory Assets	1,000	3,503
Other regulatory assets
Regulatory Assets and Liabilities
Regulatory Assets	$ 1,431	$ 1,768