Contingencies: (Details) - GSWC customer in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) customer
Environmental Clean-Up and Remediation
Contingencies
Amount spent in clean-up and remediation activities	$ 5.1
Amount paid by the State of California Underground Storage Tank Fund for clean-up and remediation of plant facilities	1.5
Accrued liability for the estimated additional cost to complete the clean-up at the site	$ 1.4
City of Claremont | Condemnation of Properties
Contingencies
Number of customers served through water systems | customer	11
Ojai FLOW | Condemnation of Properties
Contingencies
Number of customers served through water systems | customer	3
Independent Transmission and Distribution System | City of Claremont | Condemnation of Properties
Contingencies
Public utilities, property, plant and equipment, net	$ 49.3
Independent Transmission and Distribution System | Ojai FLOW | Condemnation of Properties
Contingencies
Public utilities, property, plant and equipment, net	$ 22.4
Maximum | Independent Transmission and Distribution System | City of Claremont | Condemnation of Properties
Contingencies
Timing of court decision on condemnation matter	90 days