LONG-TERM DEBT (Details) - USD ($)	Jun. 11, 2019	Oct. 04, 2011	Dec. 31, 2020	Dec. 31, 2019
Long-term debt
Unamortized debt issuance costs			$ (4,490,000)	$ (4,693,000)
Total long-term debt			786,227,000	808,622,000
Current maturities of long-term debt, net			5,127,000	21,868,000
Long-term debt, net			781,100,000	786,754,000
Capital lease liability			5,204,000	5,885,000
Cal Water
Long-term debt
Debt maturity period		15 years
Capital lease liability			4,600,000
Capital lease liability				5,200,000
Mortgages | Cal Water
Long-term debt
Debt issued	$ 400,000,000.0
Mortgages | Series UUU | Cal Water
Long-term debt
Repayment of debt	$ 300,000,000.0
Mortgages | Series VVV | Cal Water
Long-term debt
Interest rate	3.40%
Debt issued	$ 100,000,000.0
Mortgages | Series WWW | Cal Water
Long-term debt
Interest rate	4.07%
Debt issued	$ 100,000,000.0
Mortgages | Series YYY | Cal Water
Long-term debt
Interest rate	4.17%
Debt issued	$ 200,000,000.0
First Mortgage
Long-term debt
Long-term debt			$ 780,000,000	801,246,000
First Mortgage Bonds YYY Series Due 2059
Long-term debt
Interest rate			4.17%
Long-term debt			$ 200,000,000	200,000,000
First Mortgage Bonds WWW Series Due 2049
Long-term debt
Interest rate			4.07%
Long-term debt			$ 100,000,000	100,000,000
First Mortgage Bonds VVV Series Due 2029
Long-term debt
Interest rate			3.40%
Long-term debt			$ 100,000,000	100,000,000
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 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 GGG Series, Due 2022
Long-term debt
Interest rate			5.29%
Long-term debt			$ 3,636,000	5,455,000
First Mortgage Bonds HHH Series, Due 2022
Long-term debt
Interest rate			5.29%
Long-term debt			$ 3,636,000	5,455,000
First Mortgage Bonds III Series, Due 2023
Long-term debt
Interest rate			5.54%
Long-term debt			$ 2,728,000	3,636,000
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			$ 0	16,700,000
California Department of Water Resources Loans
Long-term debt
Long-term debt			$ 5,148,000	5,604,000
California Department of Water Resources Loans | Minimum
Long-term debt
Interest rate			3.00%
Other Long-term Debt
Long-term debt
Long-term debt			$ 5,569,000	$ 6,465,000