COMMITMENTS AND CONTINGENCIES (Detail 2) $ in Thousands		12 Months Ended
	Dec. 20, 2017 USD ($) well	Dec. 31, 2018 USD ($) entity $ / acrefoot acrefoot	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Long-term purchase commitments - other disclosures
Proceeds from legal settlements		$ 0	$ 56,004	$ 0
Contingency loss recognized liability		2,300
Santa Clara Valley Water District
Long-term purchase commitments - other disclosures
Annual cost		9,700	9,100	8,500
Stockton East Water District (SEWD)
Long-term purchase commitments - other disclosures
Annual cost		$ 13,700	$ 14,100	$ 12,200
Kern County Water Agency (Agency)
Long-term purchase commitments - other disclosures
Minimum acre feet of treated water to be purchased per year over life of contract | acrefoot		20,500
Minimum acre feet of treated water to be purchased under prior agreement | $ / acrefoot		11,500
Number of other parties obligated to purchase treated water | entity		3
Minimum acre feet of treated water to be purchased per year by other parties | acrefoot		32,500
Total obligation of all parties, excluding the Company		$ 82,400
Total capital facilities charge and treated water charge obligation		$ 9,700
Total capital facilities charge and treated water charge obligation per acre foot | $ / acrefoot		473.42
Total treated water charge		$ 3,500
Portion of estimated operating cost per acre foot for treated water delivered | $ / acrefoot		64.21
California Water Service Company and City of Bakersfield v. The Dow Chemical Company, et al., Civil Case No. CIV-470999 (TCP Action) [Member]
Long-term purchase commitments - other disclosures
Amount awarded	$ 85,000
Proceeds from legal settlements	$ 56,000	$ 43,900
Claims settled | well	47
Total claims | well	57
Release from future claims | well	36