Regulatory Matters: (Details) (USD $)	Mar. 31, 2013	Dec. 31, 2012
Regulatory matters:
Regulatory asset not accruing carrying costs	$ 75,400,000
Pension and other post-retirement obligations
Regulatory matters:
Regulatory asset not accruing carrying costs	51,600,000
Flow-through taxes, net
Regulatory matters:
Regulatory asset not accruing carrying costs	16,000,000
Memorandum account to track unrealized gains and losses on purchase power contracts
Regulatory matters:
Regulatory asset not accruing carrying costs	1,500,000
GOLDEN STATE WATER COMPANY
Regulatory matters:
Regulatory Assets	185,229,000	176,015,000
GOLDEN STATE WATER COMPANY | Various refunds to customers
Regulatory matters:
Regulatory Assets	(6,522,000)	(7,558,000)
GOLDEN STATE WATER COMPANY | WRAM, net of MCBA
Regulatory matters:
Regulatory Assets	44,449,000	42,574,000
GOLDEN STATE WATER COMPANY | Base revenue requirement adjustment mechanism
Regulatory matters:
Regulatory Assets	7,270,000	6,833,000
GOLDEN STATE WATER COMPANY | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Regulatory Assets	15,831,000	16,030,000
GOLDEN STATE WATER COMPANY | Pension and other post-retirement obligations
Regulatory matters:
Regulatory Assets	56,484,000	56,894,000
GOLDEN STATE WATER COMPANY | Flow-through taxes, net
Regulatory matters:
Regulatory Assets	16,010,000	16,415,000
GOLDEN STATE WATER COMPANY | General rate case memorandum accounts
Regulatory matters:
Regulatory Assets	11,427,000	4,495,000
GOLDEN STATE WATER COMPANY | Other regulatory assets, net
Regulatory matters:
Regulatory Assets	$ 40,280,000	$ 40,332,000