Regulatory Matters: Alternative-Revenue Programs (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Increase (decrease) in other regulatory assets	$ 3,700
GOLDEN STATE WATER COMPANY
Regulatory matters:
Under (over) collection	$ (4,728)		$ 2,042
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Commercial paper, term	90 days
Amount billed to customers as surcharges	$ 4,200	$ 4,000
Under (over) collection	$ 29,011		$ 29,556
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account | Minimum
Regulatory matters:
Recovery Period for under Collection, Balances Greater than 15 Percent of Adopted Annual Revenues			12 months
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account | Maximum
Regulatory matters:
Regulatory asset recovery periods	24 months
Recovery Period for under Collection, Balances Greater than 15 Percent of Adopted Annual Revenues			24 months
GOLDEN STATE WATER COMPANY | WRAM
Regulatory matters:
Under (over) collection	$ 3,300
GOLDEN STATE WATER COMPANY | Modified Cost Balancing Account
Regulatory matters:
Under (over) collection	$ 25,700