Regulatory Matters (Details) - USD ($) $ in Thousands	1 Months Ended		12 Months Ended
	Oct. 31, 2005	Jul. 31, 2005	Dec. 31, 2016	Dec. 31, 2015
Regulatory matters:
Regulatory Asset Not Accruing Carrying Costs			$ 56,900
Pension Costs and Other Postretirement Benefit Costs
Regulatory matters:
Regulatory Asset Not Accruing Carrying Costs			26,800
General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Total			9,500
GSWC
Regulatory matters:
Total			146,281	$ 132,696
GSWC | Various refunds to customers
Regulatory matters:
Total			(5,866)	(4,766)
GSWC | WRAM, net of MCBA
Regulatory matters:
Total			47,340	45,171
GSWC | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Total			11,820	12,699
Regulatory Asset Recovery Periods		20 years
GSWC | Pension Costs and Other Postretirement Benefit Costs
Regulatory matters:
Total			28,118	21,996
GSWC | Gain (Loss) on Derivative Instruments [Member]
Regulatory matters:
Total			4,901	7,053
GSWC | Flow-through taxes, net
Regulatory matters:
Total			20,134	16,176
GSWC | Low income rate assistance balancing accounts
Regulatory matters:
Total			8,272	8,699
GSWC | Other regulatory assets, net
Regulatory matters:
Total			17,633	21,235
GSWC | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Total			$ 13,929	$ 4,433
Minimum [Member] | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Regulatory Asset Recovery Periods			12 months
Minimum [Member] | GSWC | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Regulatory Asset Recovery Periods			12 months
Maximum [Member] | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Regulatory Asset Recovery Periods			24 months
Maximum [Member] | GSWC | Costs deferred for future recovery on Aerojet case
Regulatory matters:
Regulatory Asset Recovery Periods	20 years
Maximum [Member] | GSWC | General Rate Case Memorandum Accounts [Member]
Regulatory matters:
Regulatory Asset Recovery Periods			24 months