LONG-TERM DEBT (Details) - USD ($)			12 Months Ended
	Sep. 13, 2018	Oct. 04, 2011	Dec. 31, 2018	Dec. 31, 2017	Nov. 17, 2010	Apr. 17, 2009
Long-term debt
Unamortized debt issuance costs			$ (3,762,000)	$ (3,889,000)
Total long-term debt			814,938,000	531,713,000
Current maturities of long-term debt, net			104,911,000	15,920,000
Long-term debt, net			710,027,000	515,793,000
Cal Water
Long-term debt
Debt maturity period		15 years
Capital lease liability			5,800,000	6,400,000
First Mortgage
Long-term debt
Long-term debt			$ 805,892,000	521,445,000
First Mortgage Bonds TTT Series Due 2056
Long-term debt
Interest rate			4.61%
Long-term debt			$ 10,000,000	10,000,000
First Mortgage Bonds SSS Series Due 2046
Long-term debt
Interest rate			4.41%
Long-term debt			$ 40,000,000	40,000,000
First Mortgage Bonds QQQ Series Due 2025
Long-term debt
Interest rate			3.33%
Long-term debt			$ 50,000,000	50,000,000
First Mortgage Bonds RRR Series Due 2045
Long-term debt
Interest rate			4.31%
Long-term debt			$ 50,000,000	50,000,000
First Mortgage Bonds PPP Series, due 2040
Long-term debt
Interest rate			5.50%
Long-term debt			$ 100,000,000	100,000,000
First Mortgage Bonds PPP Series, due 2040 | Cal Water
Long-term debt
Debt issued					$ 100,000,000
Interest rate					5.50%
First Mortgage Bonds LL Series, due 2019
Long-term debt
Interest rate			5.875%
Long-term debt			$ 100,000,000	100,000,000
First Mortgage Bonds LL Series, due 2019 | Cal Water
Long-term debt
Debt issued						$ 100,000,000
Interest rate						5.875%
First Mortgage Bonds UUU Series, due 2020
Long-term debt
Long-term debt			$ 300,000,000	0
First Mortgage Bonds AAA Series, due in 2025
Long-term debt
Interest rate			7.28%
Long-term debt			$ 20,000,000	20,000,000
First Mortgage Bonds BBB Series, due in 2028
Long-term debt
Interest rate			6.77%
Long-term debt			$ 20,000,000	20,000,000
First Mortgage Bonds CCC Series, Due 2030
Long-term debt
Interest rate			8.15%
Long-term debt			$ 20,000,000	20,000,000
First Mortgage Bonds DDD Series, Due 2031
Long-term debt
Interest rate			7.13%
Long-term debt			$ 20,000,000	20,000,000
First Mortgage Bonds EEE Series, Due 2032
Long-term debt
Interest rate			7.11%
Long-term debt			$ 20,000,000	20,000,000
First Mortgage Bonds FFF Series Due 2017 | Cal Water
Long-term debt
Repayment of debt			$ 20,000,000
First Mortgage Bonds GGG Series, Due 2022
Long-term debt
Interest rate			5.29%
Long-term debt			$ 7,273,000	9,091,000
First Mortgage Bonds HHH Series, Due 2022
Long-term debt
Interest rate			5.29%
Long-term debt			$ 7,273,000	9,091,000
First Mortgage Bonds III Series, Due 2023
Long-term debt
Interest rate			5.54%
Long-term debt			$ 4,546,000	5,454,000
First Mortgage Bonds JJJ Series, Due 2018
Long-term debt
Interest rate			5.44%
Long-term debt			$ 0	909,000
First Mortgage Bonds LLL Series, Due 2018
Long-term debt
Interest rate			5.48%
Long-term debt			$ 0	10,000,000
First Mortgage Bonds OOO Series, Due 2031
Long-term debt
Interest rate			6.02%
Long-term debt			$ 20,000,000	20,000,000
First Mortgage Bonds CC Series, Due 2020
Long-term debt
Interest rate			9.86%
Long-term debt			$ 16,800,000	16,900,000
First Mortgage Bond JJJ and LLL | Cal Water
Long-term debt
Repayment of debt			10,900,000
California Department of Water Resources Loans
Long-term debt
Long-term debt			5,830,000	6,201,000
Other Long-term Debt
Long-term debt
Long-term debt			$ 6,978,000	$ 7,956,000
Minimum | California Department of Water Resources Loans
Long-term debt
Interest rate			2.60%	2.60%
Maximum | California Department of Water Resources Loans
Long-term debt
Interest rate			8.00%	8.00%
First Mortgage Bonds due 2020 [Member] | Secured Debt [Member]
Long-term debt
Debt issued	$ 300,000,000.0
LIBOR | First Mortgage Bonds due 2020 [Member] | Secured Debt [Member]
Long-term debt
Interest rate margin (as a percent)	0.70%
Redemption price	102.00%