Taxes on Income (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Taxes on income
Unrecognized Tax Benefits	$ 0	$ 0	$ 0
Deferred tax assets:
Regulatory-liability-related	28,851,000	32,042,000
Contributions and advances	6,768,000	6,660,000
Deferred Tax Assets, Other	5,801,000	5,924,000
Deferred tax assets	41,420,000	44,626,000
Deferred tax liabilities:
Fixed assets	(169,666,000)	(161,820,000)
Regulatory-asset-related: depreciation and other	(43,149,000)	(36,337,000)
Balancing and memorandum accounts (non-flow-through)	(8,778,000)	(8,046,000)
Deferred tax liabilities	(221,593,000)	(206,203,000)
Accumulated deferred income taxes - net	(180,173,000)	(161,577,000)
Current
Federal	19,680,000	26,327,000	14,845,000
State	8,451,000	10,489,000	6,016,000
Total current tax expense	28,131,000	36,816,000	20,861,000
Deferred
Federal	1,656,000	4,157,000	2,991,000
State	386,000	626,000	(188,000)
Total deferred tax (benefit) expense	2,042,000	4,783,000	2,803,000
Reconciliations of the effective tax rates to the federal statutory rate
Federal taxes on pretax income at statutory rate	31,383,000	34,969,000	21,433,000
Increase (decrease) in taxes resulting from:	6,508,000	9,785,000	4,335,000
Excess deferred tax amortization	(1,467,000)	(1,648,000)	(1,311,000)
Flow-through on fixed assets	1,075,000	1,067,000	1,076,000
Flow-through on removal costs	(3,096,000)	(2,255,000)	(1,802,000)
Tax Adjustments, Release of Regulatory Liability	(5,015,000)	0	0
Investment tax credit	(69,000)	(71,000)	(71,000)
Other- net	854,000	(248,000)	4,000
Total income tax expense operations	30,173,000	41,599,000	23,664,000
Income before income taxes	$ 149,441,000	$ 166,520,000	$ 102,060,000
Effective income tax rate (as a percent)	20.20%	25.00%	23.20%
Income tax effect, excess deferred income taxes estimate change	$ 5,000,000
GSWC
Deferred tax assets:
Regulatory-liability-related	27,171,000	$ 30,407,000
Contributions and advances	7,103,000	6,981,000
Deferred Tax Assets, Other	5,632,000	6,041,000
Deferred tax assets	39,906,000	43,429,000
Deferred tax liabilities:
Fixed assets	(162,366,000)	(155,131,000)
Regulatory-asset-related: depreciation and other	(39,635,000)	(33,242,000)
Balancing and memorandum accounts (non-flow-through)	(4,315,000)	(2,514,000)
Deferred tax liabilities	(206,316,000)	(190,887,000)
Accumulated deferred income taxes - net	(166,410,000)	(147,458,000)
Current
Federal	13,570,000	22,564,000	$ 10,582,000
State	6,551,000	10,176,000	4,909,000
Total current tax expense	20,121,000	32,740,000	15,491,000
Deferred
Federal	1,362,000	2,867,000	1,507,000
State	1,386,000	82,000	(652,000)
Total deferred tax (benefit) expense	2,748,000	2,949,000	855,000
Reconciliations of the effective tax rates to the federal statutory rate
Federal taxes on pretax income at statutory rate	24,640,000	29,063,000	14,724,000
Increase (decrease) in taxes resulting from:	5,772,000	9,169,000	3,119,000
Excess deferred tax amortization	(1,491,000)	(1,681,000)	(1,130,000)
Flow-through on fixed assets	1,058,000	1,041,000	1,010,000
Flow-through on removal costs	(3,029,000)	(2,225,000)	(1,715,000)
Tax Adjustments, Release of Regulatory Liability	(5,015,000)	0	0
Investment tax credit	(69,000)	(71,000)	(71,000)
Other- net	1,003,000	393,000	409,000
Total income tax expense operations	22,869,000	35,689,000	16,346,000
Income before income taxes	$ 117,332,000	$ 138,397,000	$ 70,116,000
Effective income tax rate (as a percent)	19.50%	25.80%	23.30%