SHORT-TERM BORROWINGS (Details) - USD ($)			12 Months Ended
	Mar. 10, 2015	Oct. 04, 2011	Dec. 31, 2015	Dec. 31, 2014
Borrowings under the bank lines of credit
Maximum short-term borrowings			$ 139,582,000	$ 82,668,000
Average amount outstanding			$ 104,863,000	$ 69,267,000
Weighted average interest rate			1.04%	1.15%
Interest rate at December 31			1.03%	1.12%
Revolving Credit Facility [Member]
Short-term borrowings
Maximum borrowing capacity	$ 450,000,000
Debt maturity period	5 years
Revolving Credit Facility [Member] | Minimum
Short-term borrowings
Commitment fee (as a percent)	8.00%
Revolving Credit Facility [Member] | Maximum
Short-term borrowings
Commitment fee (as a percent)	12.50%
Revolving Credit Facility [Member] | LIBOR | Minimum
Short-term borrowings
Interest rate margin (as a percent)	72.50%
Revolving Credit Facility [Member] | LIBOR | Maximum
Short-term borrowings
Interest rate margin (as a percent)	95.00%
Parent Company
Short-term borrowings
Amount outstanding under line of credit			$ 33,600,000	$ 61,700,000
Parent Company | Revolving Credit Facility [Member]
Short-term borrowings
Maximum borrowing capacity	$ 150,000,000
Cal Water
Short-term borrowings
Debt maturity period		15 years
Amount outstanding under line of credit			$ 0	$ 17,400,000
Cal Water | Revolving Credit Facility [Member]
Short-term borrowings
Maximum borrowing capacity	$ 300,000,000
Period within which borrowings are to be repaid	12 months
Additional capacity available	$ 50,000,000