LONG-TERM DEBT (Details) - USD ($)	Oct. 04, 2011	Dec. 31, 2016	Mar. 16, 2016	Dec. 31, 2015	Oct. 13, 2015	Nov. 17, 2010	Apr. 17, 2009
Long-term debt
Unamortized debt issuance costs		$ (4,475,000)		$ (4,842,000)
Total long-term debt		557,953,000		514,045,000
Current maturities of long-term debt		26,208,000		6,043,000
Long-term debt, less current maturities		531,745,000		508,002,000
Cal Water
Long-term debt
Current maturities of long-term debt		25,657,000		5,654,000
Long-term debt, less current maturities		530,850,000		507,034,000
Debt maturity period	15 years
Capital lease liability		7,000,000		7,500,000
First Mortgage
Long-term debt
Long-term debt		$ 547,000,000		502,554,000
First Mortgage | Cal Water
Long-term debt
Debt issued			$ 50,000,000		$ 100,000,000.0
First Mortgage Bonds TTT Series Due 2056 [Member]
Long-term debt
Interest rate		4.61%
Long-term debt		$ 10,000,000		0
First Mortgage Bonds SSS Series Due 2046 [Member]
Long-term debt
Interest rate		4.41%
Long-term debt		$ 40,000,000		0
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
Interest rate						5.50%
Debt issued						$ 100,000,000
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
Interest rate							5.875%
Debt issued							$ 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 FFF Series, Due 2017
Long-term debt
Interest rate		5.90%
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		$ 10,909,000		12,727,000
First Mortgage Bonds HHH Series, Due 2022
Long-term debt
Interest rate		5.29%
Long-term debt		$ 10,909,000		12,727,000
First Mortgage Bonds III Series, Due 2023
Long-term debt
Interest rate		5.54%
Long-term debt		$ 6,364,000		7,273,000
First Mortgage Bonds JJJ Series, Due 2018
Long-term debt
Interest rate		5.44%
Long-term debt		$ 1,818,000		2,727,000
First Mortgage Bonds LLL Series, Due 2018
Long-term debt
Interest rate		5.48%
Long-term debt		$ 10,000,000		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		$ 17,000,000		17,100,000
California Department of Water Resources Loans
Long-term debt
Long-term debt		6,519,000		6,857,000
Other Long-term Debt
Long-term debt
Long-term debt		$ 8,909,000		$ 9,476,000
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%