Taxes on Income (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Taxes on income
Unrecognized Tax Benefits	$ 0	$ 0	$ 0
Deferred tax assets:
Regulatory-liability-related	32,042,000	31,330,000
Contributions and advances	6,660,000	6,544,000
Deferred Tax Assets, Other	5,924,000	7,424,000
Deferred tax assets	44,626,000	45,298,000
Deferred tax liabilities:
Fixed assets	(161,820,000)	(155,955,000)
Regulatory-asset-related: depreciation and other	(36,337,000)	(30,226,000)
Balancing and memorandum accounts (non-flow-through)	(8,046,000)	(8,794,000)
Deferred tax liabilities	(206,203,000)	(194,975,000)
Accumulated deferred income taxes - net	(161,577,000)	(149,677,000)
Current
Federal	26,327,000	14,845,000	19,592,000
State	10,489,000	6,016,000	7,270,000
Total current tax expense	36,816,000	20,861,000	26,862,000
Deferred
Federal	4,157,000	2,991,000	2,802,000
State	626,000	(188,000)	759,000
Total deferred tax (benefit) expense	4,783,000	2,803,000	3,561,000
Reconciliations of the effective tax rates to the federal statutory rate
Federal taxes on pretax income at statutory rate	34,969,000	21,433,000	26,202,000
Increase (decrease) in taxes resulting from:	9,785,000	4,335,000	6,425,000
Excess deferred tax amortization	(1,648,000)	(1,311,000)	(1,356,000)
Flow-through on fixed assets	1,067,000	1,076,000	1,069,000
Flow-through on removal costs	(2,255,000)	(1,802,000)	(1,962,000)
Investment tax credit	(71,000)	(71,000)	(71,000)
Other- net	(248,000)	4,000	116,000
Total income tax expense operations	41,599,000	23,664,000	30,423,000
Income before income taxes	$ 166,520,000	$ 102,060,000	$ 124,770,000
Effective income tax rate (as a percent)	25.00%	23.20%	24.40%
GSWC
Deferred tax assets:
Regulatory-liability-related	$ 30,407,000	$ 29,623,000
Contributions and advances	6,981,000	6,896,000
Deferred Tax Assets, Other	6,041,000	7,874,000
Deferred tax assets	43,429,000	44,393,000
Deferred tax liabilities:
Fixed assets	(155,131,000)	(150,133,000)
Regulatory-asset-related: depreciation and other	(33,242,000)	(28,489,000)
Balancing and memorandum accounts (non-flow-through)	(2,514,000)	(4,559,000)
Deferred tax liabilities	(190,887,000)	(183,181,000)
Accumulated deferred income taxes - net	(147,458,000)	(138,788,000)
Current
Federal	22,564,000	10,582,000	$ 13,698,000
State	10,176,000	4,909,000	6,089,000
Total current tax expense	32,740,000	15,491,000	19,787,000
Deferred
Federal	2,867,000	1,507,000	2,251,000
State	82,000	(652,000)	57,000
Total deferred tax (benefit) expense	2,949,000	855,000	2,308,000
Reconciliations of the effective tax rates to the federal statutory rate
Federal taxes on pretax income at statutory rate	29,063,000	14,724,000	19,175,000
Increase (decrease) in taxes resulting from:	9,169,000	3,119,000	4,923,000
Excess deferred tax amortization	(1,681,000)	(1,130,000)	(1,184,000)
Flow-through on fixed assets	1,041,000	1,010,000	1,008,000
Flow-through on removal costs	(2,225,000)	(1,715,000)	(1,954,000)
Investment tax credit	(71,000)	(71,000)	(71,000)
Other- net	393,000	409,000	198,000
Total income tax expense operations	35,689,000	16,346,000	22,095,000
Income before income taxes	$ 138,397,000	$ 70,116,000	$ 91,310,000
Effective income tax rate (as a percent)	25.80%	23.30%	24.20%