SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 1) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									$ 674,736	$ 622,474	$ 589,528
Regulatory balancing account revenue									23,460	53,639	19,842
Total operating revenue	$ 167,417	$ 221,288	$ 174,938	$ 134,553	$ 164,296	$ 214,037	$ 173,438	$ 124,342	698,196	676,113	609,370
Total non-regulated revenue									18,272	15,898	16,585
Regulated Water and WasteWater Services
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									674,736	622,474	589,528
Total operating revenue									698,196	676,113	609,370
Residential
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									450,062	415,893	394,438
Business
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									130,041	118,279	117,510
Industrial
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									34,236	28,905	26,330
Public authorities
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									34,511	31,671	29,220
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									25,886	27,726	22,030
Operating and maintenance revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									10,258	8,621	8,430
Other non-regulated revenue
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									5,547	5,262	6,232
Non-regulated revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers									15,805	13,883	14,662
Lease revenue									2,467	2,015	1,923
Total non-regulated revenue									$ 18,272	$ 15,898	$ 16,585