Short-term and Long-term Borrowings (Details) - USD ($)	1 Months Ended	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Oct. 13, 2015
Short-term and Long-term Borrowings
Proceeds from long-term debt, net of expenses		$ 50,039,000	$ 50,000
Parent Company
Short-term and Long-term Borrowings
Proceeds from long-term debt, net of expenses		0	0
Parent Company | Revolving Credit Facility
Short-term and Long-term Borrowings
Amount outstanding under line of credit	$ 34,500,000	34,500,000		$ 33,600,000
Cal Water
Short-term and Long-term Borrowings
Proceeds from long-term debt, net of expenses		49,823,000	$ 0
Cal Water | Revolving Credit Facility
Short-term and Long-term Borrowings
Repayment of debt	48,600,000
Amount outstanding under line of credit	$ 0	$ 0
Average borrowing rate (as a percent)	1.27%	1.27%	1.09%
Cal Water | Secured Debt [Member]
Short-term and Long-term Borrowings
Debt issued					$ 150,000,000.0
Debt issuance costs	$ 300,000
Proceeds from long-term debt, net of expenses	49,700,000
Cal Water | Secured Debt [Member] | First Mortgage Bonds Issue 1 [Member]
Short-term and Long-term Borrowings
Debt issued					100,000,000.0
Cal Water | Secured Debt [Member] | Series QQQ Bond [Member]
Short-term and Long-term Borrowings
Debt issued					$ 50,000,000.0
Interest rate					3.33%
Cal Water | Secured Debt [Member] | Series RRR Bond [Member]
Short-term and Long-term Borrowings
Debt issued					$ 50,000,000.0
Interest rate					4.31%
Cal Water | Secured Debt [Member] | First Mortgage Bonds Issue 2 [Member]
Short-term and Long-term Borrowings
Debt issued	50,000,000.0	$ 50,000,000.0
Cal Water | Secured Debt [Member] | Series SSS Bond [Member]
Short-term and Long-term Borrowings
Debt issued	$ 40,000,000.0	$ 40,000,000.0
Interest rate	4.41%	4.41%
Cal Water | Secured Debt [Member] | Series TTT Bond [Member]
Short-term and Long-term Borrowings
Debt issued	$ 10,000,000.0	$ 10,000,000.0
Interest rate	4.61%	4.61%