Regulatory Matters: (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Apr. 30, 2012	Dec. 31, 2015	Mar. 31, 2017	Dec. 31, 2016
Regulatory matters:
Regulatory Asset Not Accruing Carrying Costs			$ 58,000
Weighted Cost of Capital Percent			8.34%
Settlement Agreement Proposed Authorized Return on Equity Percentage			9.43%
Pension and other post-retirement obligations
Regulatory matters:
Regulatory Asset Not Accruing Carrying Costs			$ 26,600
Flow-through taxes, net
Regulatory matters:
Regulatory assets			20,708
Regulatory Asset Not Accruing Carrying Costs			20,700
GOLDEN STATE WATER COMPANY
Regulatory matters:
Regulatory assets			155,987	$ 146,281
GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Regulatory assets			55,298	47,340
annual surcharges as percentage of last authorized revenue requirement	10.00%
GOLDEN STATE WATER COMPANY | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Regulatory assets			11,705	11,820
GOLDEN STATE WATER COMPANY | Pension and other post-retirement obligations
Regulatory matters:
Regulatory assets			27,452	28,118
GOLDEN STATE WATER COMPANY | Derivative unrealized loss
Regulatory matters:
Regulatory assets			5,460	4,901
GOLDEN STATE WATER COMPANY | Flow-through taxes, net
Regulatory matters:
Regulatory assets				20,134
GOLDEN STATE WATER COMPANY | Low income rate assistance balancing accounts
Regulatory matters:
Regulatory assets			8,502	8,272
GOLDEN STATE WATER COMPANY | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Regulatory assets			14,689	13,929
GOLDEN STATE WATER COMPANY | Other regulatory assets
Regulatory matters:
Regulatory assets			$ 17,477	17,633
GOLDEN STATE WATER COMPANY | Cost of Capital, Proceeding for Water Regions [Member]
Regulatory matters:
Weighted Cost of Capital Percent			9.11%
Cost Of Debt Percent			6.60%
Return on Equity Percentage			11.00%
Water Service Utility Operations [Member] | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Regulatory assets			$ 10,200
Various refunds to customers | GOLDEN STATE WATER COMPANY
Regulatory matters:
Regulatory assets			$ (5,304)	$ (5,866)
Maximum [Member] | GOLDEN STATE WATER COMPANY | Water Revenue Adjustment Mechanism, net of Modified Cost Balancing Account
Regulatory matters:
Regulatory Asset Recovery Periods		24 months