SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 6) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Regulatory Assets and Liabilities
Regulatory Assets	$ 361,893	$ 390,331
Regulatory Liabilities	35,264	36,447
Short-term portion of the regulatory assets	35,052	53,199
Short-term portion of the regulatory liabilities	2,227	6,126
Long-Term Debt Premium, Discount and Expense
Amortization expense included in interest expense	825	797	$ 1,081
Advances for Construction
Advances for construction	$ 180,172	182,284
Refund period	40 years
Estimated refunds of advances
2016	$ 7,900
2017	7,700
2018	7,700
2019	7,600
2020	7,600
Future tax benefits due ratepayers
Regulatory Assets and Liabilities
Regulatory Liabilities	29,505	26,114
Conservation program
Regulatory Assets and Liabilities
Regulatory Liabilities	2,317	2,669
Pension balancing account
Regulatory Assets and Liabilities
Regulatory Liabilities	792	4,291
Other Liabilities
Regulatory Assets and Liabilities
Regulatory Liabilities	2,650	3,373
Pension and retiree group health
Regulatory Assets and Liabilities
Regulatory Assets	205,614	245,008
Future tax benefits due ratepayers
Regulatory Assets and Liabilities
Regulatory Assets	81,522	72,350
Other accrued benefits
Regulatory Assets and Liabilities
Regulatory Assets	27,327	32,959
Interim rates long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory Assets	5,238	10,627
Net WRAM and MCBA long-term accounts receivable
Regulatory Assets and Liabilities
Regulatory Assets	15,410	14,449
Asset retirement obligations, net
Regulatory Assets and Liabilities
Regulatory Assets	14,682	13,863
Tank Coating
Regulatory Assets and Liabilities
Regulatory Assets	6,829	0
Health care balancing account
Regulatory Assets and Liabilities
Regulatory Assets	3,503	1,075
Other regulatory assets
Regulatory Assets and Liabilities
Regulatory Assets	$ 1,768	$ 0