Regulatory Matters: Alternative-Revenue Programs (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Apr. 30, 2012	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
WRAM, net of MCBA
Regulatory matters:
Increase (decrease) in other regulatory assets		$ 11,600
WRAM, net of MCBA | Maximum
Regulatory matters:
WRAM and MCBA Recovery Period		24 months
GOLDEN STATE WATER COMPANY
Regulatory matters:
Net Regulatory Assets		$ 155,987		$ 146,281
GOLDEN STATE WATER COMPANY | WRAM, net of MCBA
Regulatory matters:
Commercial paper, term		90 days
Amount billed to customers as surcharges		$ 4,000	$ 1,400
Net Regulatory Assets		$ 55,298		$ 47,340
Under Collection Balances as Percentage of Adopted Annual Revenues	15.00%
annual surcharges as percentage of last authorized revenue requirement	10.00%
GOLDEN STATE WATER COMPANY | WRAM, net of MCBA | Minimum
Regulatory matters:
Recovery Period for under Collection, Balances Greater than 15 Percent of Adopted Annual Revenues	19 months
WRAM and MCBA Recovery Period		P12M
GOLDEN STATE WATER COMPANY | WRAM, net of MCBA | Maximum
Regulatory matters:
Alternative Revenue Program				24 months
Recovery Period for under Collection, Balances Greater than 15 Percent of Adopted Annual Revenues				18 months
Recovery Period for under Collection Balances that are up to 15 Percent of Adopted Annual Revenues	36 months
WRAM and MCBA Recovery Period		P18M
Regulatory Asset Recovery Periods					24 months
GOLDEN STATE WATER COMPANY | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Net Regulatory Assets		$ 14,689		$ 13,929
GOLDEN STATE WATER COMPANY | WRAM
Regulatory matters:
Deferred Revenue		320		$ 910	$ 1,400
Net Regulatory Assets		40,000
GOLDEN STATE WATER COMPANY | Modified Cost Balancing Account
Regulatory matters:
Net Regulatory Assets		$ 15,300